In answer to your question, yes, the Churchill was a highly effective design. This is not effectively conveyed in many computer games, such as World of Tanks or War Thunder, because they abstract the role of tanks into one of engaging other tanks, and often arbitrarily rank the vehicles based on raw statistics, which ignores the many nuances of tank design and deployment, which often means that the Churchill suffers due to its rather idiosyncratic design.

The Churchill was designed as a successor to the Matilda II and Valentine tanks, and was part of the 'infantry tank' family. Vehicles in this branch of British medium tank design (as opposed to lighter, more mobile cruisers), were intended to bear heavy armour and armament sufficient to support infantry in the attack, reminiscent of the employment of armour in the First World War. For this role, the Churchill was well-suited: its long body gave it great obstacle crossing capability and hill-climbing, and it was incredibly well-armoured and robust, which also made it a great platform for engineering and specialist vehicles. It benefitted from the Merritt-Brown triple differential transmission, which also made it comparatively nimble for such an ungainly vehicle, as well as a simple, flat-plate/cast design that made production easier. However, there were some initial flaws in the design, which largely resulted from the need to produce the vehicle as fast as possible to make good the losses the British Army sustained in the Battle of France. As a result, early models were under-powered and under-gunned, carrying the 2-pdr (40mm) tank gun, and were plagued by mechanical issues.

Once these issues were overcome however, and the tank re-armed with the 6-pdr gun, it worked highly effectively in its first few operations. Beyond the disastrous Dieppe Raid in August 1942, the Churchill gave good service in the North Africa campaign, proving highly resilient at El Alamein and then demonstrating its infantry support capabilities in Tunisia; during Operation Ochsenkopf in March 1943, a pair of Churchills climbed a steep valley to destroy a German column of several hundred men and a number of tanks and guns without loss at Steamroller Farm. From here, the Churchill would play a key role in the Army Tank Brigades in Normandy and Italy, offering vital support to the infantry they cooperated with, a crucial task, even if it may have lacked the glamour of the breakthrough cruiser tanks. The Churchill was thus an effective design for its proper task, functioning as part of a combined arms team of artillery, armour and infantry, to overwhelm Axis defences in concert.

The Churchill wasn't a good tank. Its failure in the fall of 1941 to perform even elementary functions required of a tank caused a top to bottom review of how the Ministry of Supply worked and how tanks were designed in the UK in general. At one point there was not only the danger of the Churchill being cancelled, but the entire concept of infantry tanks being scrapped in favour of "universal tanks" like the Cromwell.

The issue was, like /u/HereticalShinigami mentioned, a tank was desperately needed. Combat in France in 1940 showed that not only were the Infantry Tanks Mk.I and Mk.II obsolete, but the A20, the prospective replacement for the Mk.II, was also ill-suited for the modern battlefield.

An order was given to Vauxhall Motors to build a new tank, but the problem was that Vauxhall had never worked on tanks before. The result was absolutely disastrous. When engineers with tank experience, such as Sir Henry Ricardo and Sir Albert Stern were invited to review the design, they replied that it would be impossible to make a battleworthy tank out of it within a year, and perhaps impossible at all. Ricardo had high opinions about the skills of Vauxhall's engineers, and wrote that the result was nearly as good as one could expect for a company without experience in heavy vehicles. The lifespan of the engine was about 9 hours, the lifespan of the track links was 20 miles. The suspension had only 5 inches of travel and the tank shook violently when driving on bumpy terrain. Due to gearbox defects, the top gear could not be engaged, limiting the top speed of the tank to 10 mph.

The gun, a 2-pounder, had no advantage over the armament of the Matilda and Valentine, and the 3" howitzer in the hull was loaded and aimed by one man, which severely hampered its effectiveness. The range was also reduced due to its placement, since it could not elevate far enough.

The armour, a big point for an infantry tank, was not very good. The turret armour proved brittle and cracked under heavy 2-pounder attack. Considering that the enemy was fielding 50 mm anti-tank guns, this was grossly insufficient for a modern tank. The hull was also archaic, composed of a thick 2.5" plate bolted to a thinner 0.5" plate that was in turn bolted to a mild steel frame. This armour also came apart under 2-pounder gun fire, even though the main plate was not penetrated. This armour was also ruined by a multitude of hatches and ports that cluttered up every available surface and weakened the main plate. It was noted that a welded hull was desired, but due to the hurry that the tank was made in, the designers went with a tried and true technology.

Exercise Bumper, held in September of 1941, was nearly the final nail in the Churchill's coffin. During the 4 day exercise simulating a German invasion, 40 out of 54 Churchill tanks that took part in it broke down, and this is completely without enemy contact. The poor results of this exercise were discussed quite frequently in the Cabinet. However, this is where the Churchill was ultimately salvaged: experts estimated that a replacement infantry tank would take 18 months to design, and it was ultimately agreed that production of a second rate tank was better than no tank at all. A wide scale modernization program was launched. While the first 300 Churchills were deemed unsalvageable and left as training tanks for mechanics to cut their teeth on, the subsequent ones went through a thorough modernization program that would allow them to run 60 miles per day, 6 days a week. This was quite low for most tanks in WWII, but the Churchill was first and foremost meant for defense of the British Isles from invasion, and that was considered enough.

Sources:

Library and Archives Canada, RG 24 C 2 reel T-17885 slide 1848

Library and Archives Canada, RG 24 C 2 reel T-17885 slide 1877

Library and Archives Canada, RG 24 C 2 reel T-17885 slide 1885

Library and Archives Canada, RG 24 C 2 reel T-17885 slide 1900

The National Archives CAB 63/164 Design and Production of Heavy Tanks

The National Archives CAB 63/165 Design and Production of Heavy Tanks