This is a very good question. Just a note that I'm going to answer it specifically in terms of "how does current history compare to the history as presented in 'World At War'" as opposed to "what are big-name present-day historians' opinions of the documentary specifically".

Also a note that I enjoyed the series when I first watched it decades ago (not the 1970s though), especially the episodes that deal with the Eastern Front - furthermore that those particular episodes were also used as materials in some undergraduate history courses I took.

With that said: a lot has changed in terms of the history of the Eastern Front compared to the history presented in these particular episodes. I cannot stress enough that these episodes largely present the Eastern Front through German Wehrmacht eyes, as much of the history of the Eastern Front did during the Cold War period of the 1950s-1970s. These episodes make heavy use of English-language interviews with relatively major German figures such as Walter Warlimont and Albert Speer (while neglecting to mention their convictions for war crimes, might I add). In contrast, the Soviet side is represented by an English-language interview with Grigory Tokaty, who is, well, not no one (he was a Soviet scientist during the war), but was clearly chosen because he spoke English and was living in the UK in the time. Keep in mind that this means that extremely major Soviet figures such as Molotov, Zhukov, Malenkov, Mikoyan, or Semyon Timoshenko, all of whom were alive in 1970, are not interviewed (NB - I guess one of the episodes has an interview with Colonel General Lyudnikov, so I guess that's something). Which is not to say that a documentary team from a private television studio in the UK could have had access to any of these figures, but merely that we need to keep in mind how lopsided the commentary is.

As such, the documentary (and interviews) skew heavily towards certain German tropes, especially the idea that "General Winter" defeated the unprepared Germans in the Battle of Moscow. The documentary also plays down (although I do believe it gives some mention) German war crimes, especially those committed by the Wehrmacht.

The opening of Soviet archives since the end of the Cold War has definitely added a much deeper layer of depth to Western scholars' understanding of the Soviet side in the war, as well as access to sites and archives that have allowed historians to re-evaluate events that both sides heavily laced with propaganda. David Glantz and Jonathan House are the go-to historians for that aspect of setting the military record straight. There also has been a lot of work done by modern historians dispelling the "good Wehmacht" myth and examining the power of Nazi ideology and the committing of war crimes among most members of the Wehrmacht (Omer Bartov and Christopher Browning stand out there).

Another note: The World at War is some 26 episodes long, but only three are solely dedicated to the Eastern front/USSR. In contrast there is an entire episode dedicated to the occupation of Holland. Which is all well and good, but it's worth remembering that among Germans alone some 80% of casualties occurred on the Eastern Front, so this documentary (like many documentaries and books in the US and UK) will disproportionately focus on Western and Southern Europe at the expense of the Eastern Front. A good (if to my mind incredibly harrowing) documentary to offset this is Russia's War: Blood Upon the Snow, which has loads of interviews with folks from the USSR during the war, and also has a companion book written by Richard Overy to go with it.

Pedantry: Laurence Olivier in The World at War keeps pronouncing "Stalin" as "Shtalin" and it kind of drives me nuts.

The ITV series is definitely one of the best series of its type and holds up really well in 2018. There are only two big demerits to it that one should be advised of before diving in.

Firstly, its coverage of the Eastern Front is a little thin. The series actually covers the Eastern Front better than its contemporaries (and, truth be told, better than many documentaries today). There are no interviews with either Molotov and Zhukov (although the latter was in very poor health during the four-year production) and the Soviet interviewees were mid-level or lower level figures. However, the restrictions of the Cold War can be overstated as this was the period of Detente. Martin Smith, who was in charge of the Soviet sections of the documentary, noted that there were no restrictions on interviews the series did conduct. That said, the bench of Soviet participants is quite thin and not up to the same level as other combatants. The series relies a little too heavily on German sources and interviews for its Eastern front coverage. This reliance in and of itself is not bad, but the voluminous scholarship of the late 1980s and 90s on the Eastern Front (eg David Glantz) has shown the extent to which the Germans overemphasized the "General Winter" and "Asiatic hordes" tropes to mask the fact that the Soviets eventually outfought their German enemies.

The second major deficit is that there is no discussion of Ultra or other codebreaking efforts. The Ultra story itself only broke a few weeks after the last episode aired with the publication of the book Ultra at War. So one can watch the series and have no idea that either the Americans were reading Japanese codes or the Anglo-Americans had broken ENIGMA. That means that some of the episodes, like the one on the Battle of the Atlantic- see this description on Uboat.net- or the Battle of Midway, are missing a really vital piece of the narrative puzzle.

However, these demerits are relatively minor in light of The World at War's many virtues. The interviews with direct participants came at the right time as many are quite candid and it's one thing to know Primo Levi from Survival in Auschwitz, but another to see him talk about the Holocaust directly. The graphics, although dated with a seventies aesthetic, are clear and intelligible (another virtue not often present in today's documentaries!), and the stentorian narration by Olivier is suitably dramatic at places. It also has an incredibly impressive scope; when I rewatched it just a few years ago, I was surprised at just how much of the war it covers.