I only have a few seasons under my belt (some pre, some post), so take my opinion for what it's worth.
I slightly prefer the new engine at the moment, and I hope that the remaining glitches can be worked out quickly. I really hope that we don't lose some of the veteran coaches that strongly dislike the new engine. The next five, maybe ten (maybe more?) seasons will continue to be bumpy, but I think the end result will be an improvement.
One thing I might be wise not to say, but will: I think some (not most) of the biggest complaints aren't necessarily bugs (although there are a-plenty), but frustration of having to learn the tricks and secrets of the new engine. If I had put 100 seasons learning every nook and cranny of the old, and suddenly all that accumulated knowledge and strategy was made useless or nearly useless, I'd be pretty ticked too. This is not to say that the complaints aren't justified, butI really hope that we don't lose many of the veterans, the bugs and bumps settle down soon, and HD grows. I plan on being here a while, at least.