Warhammer 40,000 - I've enjoyed almost every edition of Warhammer 40,000. (with the exception of fourth when I experimented with warmahordes briefly). With every edition change you tend to have some things you miss and other things you can't understand why it didn't always work this way. You also tend to see corrections to rules that posed a problem in the previous editions. As such shooting, assault, psychic phase and vehicles have all experienced a time when they were amazing followed by a time where they were almost irrellevant. Not only did phases of the game become more or less relevant but codexs varied in power level based on when in the release cycle they came out. In addition you had lots of rules that were shoehorned into and existing game that didn't make sense. Each time you'd get a significant outcry because something broke the game and events would make up their own rules to "fix" the edition. It was inevitable that the game needed a hard reset with all armies starting out on the same floor as far as power level and points cost.
So far I'm loving the new edition. The rules are simple and easy to follow. The biggest problem I've seen is "remembering" prior editions and many of the weird interactions just don't exist. Cover being nothing but a +1 to your armor save makes it simple and a definitive "is your model infantry is is standing on cover?" is much better than arguing over if they're in or not.
The varied movement stats give each army it's own personality and feels less forced. I love the fixed BS and WS tied to each unit and the simplified to wound chart makes so much more sense. (Even though it's similar to the old one, not having a cap gives more variation).
I'm looking forward to playing more games a will probably do a series of article discussing the evolution on my lists. Right now I'm planning on focusing on Genestealer Cult for this edition. Once they're painted and I'm happy with a few list variations I'll go back to working on my Space Marines. The Night Lords are getting shelved for the moment as I'm a bit bitter about having a cool Legion book for six months and now being back to ground zero.