I've always thought that the Panzer IV ought to be in the running for the title of "Best Tank of WW2".

It keeps getting overshadowed by T-34, late Shermans, Panther, etc, but the thing is, those are not designs that were in service in 1939. Obviously they would be better than a 1939 design, in 1945. Panzer IV was, old though it may have been, still a very viable and capable tank in 1945. This is a testament to the fundamental design of the tank from the very beginning. About the only other tank I can think of which was in service in Sept 1939 and was still in service in mid 1945 is Matilda II, and that was not of any use in Europe.

Although production went as far as the Ausf J, arguably it was the H which was the top of the line. The J was an austere variant, which ditched powered traverse, partially to reduce the resources needed to make the tank, and partially also because the space freed up by losing the motor and generator could be used by additional fuel tanks, thus reducing the vulnerability of the tank to the Allied habit of shooting up supply assets.

By the time you get to the H model, we have a 25-ton tank which is running a power train designed for an 18-ton tank. As a result, the gearing ratios were dropped, which lowered the top speed of the tank (but not to unGodly slow levels), but increased the mobility. The tank really is stretched to its limit. The armor, similarly, was not such that it could reliably stop AP rounds from most big guns on the battlefield.

However, it still had an L48 gun capable of being dangerous to pretty much anything in the Allied motor pool, and like its opponents, most anything which could kill it, it could kill. Not quite as well as a Sherman or T-34/85, perhaps, but close enough to be useful. And in the typical tank role, bearing in mind that most things on the battlefield are not armored tanks, I'm sure that American or British infantrymen on the receiving end of a Pz IV really didn't gain much satisfaction from the fact that the Sherman may have been a bit better. That 8cm of armor, two MGs, and 7.5cm cannon aiming their way were still more than a match for Garands or Brens.

So, as a result, you have a tank which is starting to get a little cramped inside with the big gun (though not so awful, given the position of the commander thus freeing up room for the gunner/loader), is a tad slower than a Western tank, and will take longer to get a shot off, but is still 'good enough' to be a serviceable weapon anywhere on the battlefield.

The problem, like all German tanks, is not in the vehicle itself so much, but in the supporting structure. It's not the easiest tank to maintain, it's certainly not the easiest tank to build. But once it's at the fight, it has to be treated with respect.