As the slew of deleted comments and continued debate in the comments suggest, this is a deeply contested issue rooted nationalist historiography in both England and Ireland. I work on medieval and early modern Ireland, so I'm most familiar with the debates in that field. So with that being said, I'll break this answer into two parts: first, a rundown of the origins of this nationalist historiography, and second, the various components of the narrative of English exploitation of Ireland -- which bits have some truth to them and which bits have been somewhat overstated.
If you're not into detailed discussions of historiography, you can skip to the next bolded line.
In the early twentieth century, there was a strong push in Irish scholarship to reject all things English. This was due in part to debates over Home Rule and independence which dominated Irish politics even before the Easter Rising, war for independence, and civil war. The memory of the famine, just a few decades previous, was also a major component -- Ireland had suffered immensely from both starvation and death on a massive scale, as well as depopulation due to emigration, and much of the devastation had been a direct result of English policy. And these contemporary issues built on two centuries of anti-Catholic legislation.
Eoin MacNeill is a prime example of the conflation of contemporary politics with the past.(1) He was a prominent medievalist who made vital contributions to the study of early Irish law and kingship. However, he was also a nationalist politician and an ardent promoter of Gaelic culture. His interpretations of early Irish society were often colored by a somewhat romanticized vision of pre-English Ireland. Edmund Curtis continued this trajectory in his history of Ireland after the Norman Conquest.(2) Curtis was an talented and prolific historian, and his scholarship, like MacNeill's, made countless contributions to the field of Irish history, but it was also wrapped up in Curtis's preoccupation with the contemporary politics of English domination over Ireland. Underlying Curtis's work is a desire to prove that England's initial conquest of Ireland was unjustified. Embedded in this narrative was the argument that Gaelic culture had survived the conquest and in fact dominated English culture across much of the island, resulting in a great deal of cultural hybridity.
In opposition to this growing school of Gaelic nationalist historians (part of a much larger Celtic revival begun in the 19th century), in 1911, Goddard Henry Orpen put out the first of what would be a massive four-volume history of Ireland after the Norman Conquest.(3) Unlike MacNeill and Curtis, who were primarily interested in the intricacies of Gaelic society and in decrying the injustice of the Norman Conquest, Orpen posited that the Norman Conquest had been a good thing for Ireland, rescuing it from its backward, tribalistic ways. MacNeill and Orpen were not only at opposite ends of the ideological spectrum, but they butted heads in reviews and speeches.
Although the works of MacNeill, Curtis, and Orpen are in some cases over a century old, this division in the scholarship remains. Medieval Irish history has, for nearly a century, been divided into historians of the Anglo-Irish "colony" (another hotly disputed topic) and historians of Gaelic society. This is not always a division along nationalist lines, but that debate rears its head every now and then. I think it's currently best represented by Brendan Bradshaw on the Gaelic side and Steven G. Ellis on the colonial side. Ellis has been a vocal critic of Gaelic nationalist historiography, arguing that it seeks out evidence to support existing assumptions that lack validity. He argues for a strong, separate colonial identity, that there was a sharp distinction between Irish and English culture. Ellis rejects the idea that the English/Anglo-Norman settlers in Ireland eventually became gaelicized, blending with native society. He also rejects the common notion of a Gaelic Resurgence in the thirteenth and fourteenth centuries, during which the Gaelic lords not only retook large swaths of land, but also experienced a sort of cultural flourishing. In sum, Ellis argues that "the adoption for late medieval Ireland of an anachronistic, Hiberno-centric perspective, with associated nationalist themes, is a conceptual trap..."(4) Bradshaw has explicitly opposed Ellis's intepretation (as have many others, although none quite so vocally as Bradshaw). Bradshaw not only takes Ellis to task on his rejection of cultural hybridity, but he also declares that "value-free history" is not something to strive for, that nationalist histories are useful and necessary.(5) Bradshaw has argued in his own work for the birth of Irish nationalism in the late middle ages/early modern period.(6)
Both Bradshaw and Ellis are fairly old, Bradshaw especially so. They don't represent the newest generation of scholars, many of whom have begun to venture away from this debate. However, they and other scholars of their generation have continued to embed nationalist historiography into the narrative of Irish history, and it's difficult to escape, even for scholars who deliberately try to avoid it.
The issue at hand -- was England cruel and exploitative?
So with this in mind, Irish history has often been cast as either a narrative of English colonialism/imperialism/exploitation or as a narrative of Irish backwardness/barbarism, from which they were rescued by the Anglo-Norman Conquest. Let's take apart some of the key events within my period in that first narrative.
The Norman Conquest -- or was it? Curtis and those who've followed him argued that the conquest of Ireland by the Anglo-Normans was unjustified and illegal. This argument was wrapped up in late 19th/early 20th century discussions of England's continued rule over Ireland. But hold up -- was there even a conquest? And were there any Anglo-Normans involved?
The whole debacle started with a fight between two Irish kings, Diarmait mac Murchada and Tiernan Ua Ruairc. Diarmait had stolen Tiernan's wife, Derbforgaill, and Tiernan had gone to his ally, Ruadrí Ua Conchobhair, who deposed Diarmait. Diarmait then went to Henry II of England to request help getting his kingdom back. Henry II wasn't interested, but gave Diarmait permission to ask around among the Welsh marcher lords. These were English/Welsh nobility who controlled the borders between Wales and England in exchange for their lands. Diarmait gained the support of Richard de Clare (also known as Strongbow) and several others, who launched an invasion that helped Diarmait get his kingdom back. In exchange for his support, Diarmait had promised Strongbow his daughter Aoife in marriage, to make Strongbow his heir. That's not exactly how Irish succession worked, but Strongbow was powerful enough to assert his claim, which on Diarmait's death, made him king of Leinster. Of course, now that one of his vassals had become a king, Henry II took an interest. He immediately sailed for Ireland to ensure that Richard submitted to him, surrendering Ireland to Henry and having it regranted as a fief rather than an independent kingdom. Henry also took the submissions of numerous Irish kings.
The real question here is how much communication there really was between Henry II and the Irish kings. Irish kingship was a different beast from English kingship. The English monarchy was fairly powerful and very centralized, and it resided in a single person. Irish kings were basically petty kings, ruling over much smaller territories and people groups. It was also a sort of stacked/hierarchical system -- a king could have numerous subkings who owed him military service ("rising out") and a certain number of cows. However, these allegiances were fluid, not permanent. So when Henry II accepted the submission of the Irish kings, he likely thought that he was receiving a submission that 1) represented a larger entity than it did and 2) was permanent, regardless of how long those kings remained in power. On the other hand, the Irish kings likely expected that they were entering into a mutual agreement which placed them on a more even footing with Henry II than it actually did.
Some have argued that Henry II knew exactly what he was doing and that he planned it all along. I don't buy that. The real conquest came when lords from England began settling in Ireland, displacing the native inhabitants, and when Ireland was set up as a lordship for Prince John, along with a more robust administrative apparatus.(7)
So was the conquest cruel/exploitative by the English? Certainly not at first -- it was sparked by an internal feud and orchestrated by an Irish king. On the other hand, it certainly paved the way for centuries of continued conquest and displacement, as well as allowing the institution of English government in Ireland.
Continued below
(1) See Eoin MacNeill, Early Irish Laws and Institutions and Phases of Irish History
(2) See Edmund Curtis, A History of Medieval Ireland and A History of Ireland: From the Earliest Times
(3) Goddard Henry Orpen, Ireland Under the Normans
(4) Steven G. Ellis, "Nationalist Historiography and the English and Gaelic Worlds in the Late Middle Ages," Irish Historical Studies 25/97 (1986): 18.
(5) Brendan Bradshaw, "Nationalism and Historical Scholarship in Modern Ireland," Irish Historical Studies 26/104: 329-351.
(6) Brendan Bradshaw, The Irish Constitutional Revolution of the Sixteenth Century (1979)
(7) The usual term for these lords is "Anglo-Norman" in the early period and "Anglo-Irish" beginning sometime in the thirteenth/fourteenth century, after they'd assimilated somewhat. Some scholars have disputed this, though, arguing that they weren't English/Norman at all. Other terms: Cambro-Norman, Anglo-Welsh, Anglo-French, etc.