I posted a topic like this when x & y were first announced and now that they're here, I figured I'd go back to it: what do you think gen 5's impact on the series was as a whole, in terms of concepts introduced, etc.?
Honestly, as much as I enjoyed gen 5, especially white 1, I felt like it has contributed the least to the series as a whole. It added a bunch of new mons, but even with no classic mons pre-elite 4, they never felt organically connected to the group (perhaps because of the initial separation), and sure enough, black/white 2 did some back pedaling. I really liked both triple and rotation battles but felt like they weren't integrated near as well as doubles, and again, didn't feel organic. The story I felt had a lot of potential but game freak wasn't able to make it work in the end. In black/white 1, I never felt like I had an answer to team plasma who basically said battles are abusive to pokemon. The whole "bonding together (through cockfighting)" thing or the "everyone's got a different opinion" response didn't work for me. When game freak was not able to provide a deep enough answer, they turned Neo Team Plasma into Team rocket II. I wish they had done something similar to tolkien's mythos with the Einar, where we find out that pokemon are essentially "angels" created to protect humans and separating the two worlds would cause chaos.
Where I find that gen 5 did have a huge impact, though, is that it seems to begin a new level of "hand-holding" in the main game to boost one's team. We saw it first with the easily acquired lucky egg and reusable TMs, and now we're seeing it with exp. all, pokemon amie, and super training. This actually serves to work in the series' favor as it balances out the newbs and the professionals, meaning entry level players can still compete in tournaments and enjoy them because they aren't losing all the time to perfect IV mons. This, I believe, is gen 5's biggest contribution to the series.