What I've found is that it can take a while to train combat skills now. I don't know if this is the case for high-leveled creatures; I hover stably at mid-level (because free player, 'kay?). But given that defence suddenly became more crucial (at least I think it did--I'm whiffing more spells and hits than I used to), a plethora of problems began to rise.
Then, there's the problem of competition. It doesn't matter which world one flips to, there'll almost always be people at hill giants, Varrock guards, GWD somewhere, and so on. For those folks, there's usually an incentive for either experience or drops, the lesser one being a simply nice add-on to the process. With the new--and somewhat peculiar--combat system, it does at least two things.
One, it induces chaos, especially with the chain or other AoE attacks (which is not necessarily a bad thing, as mayhem fireworks can be funny). Second, as competitors (sans certain clan activities and bosses, we fight alone), we collectively suffer from getting less by doing more. Before, a group of 10... shall we say, Al-Kharid warriors (for a lack of a better multi-combat opponent) would feed a group of players accordingly to their accuracy and damage output--ergo, sharper opponents with sharper weapons tend to get more experience, as they should. Now, there is no such division; it's either do-or-die--er, kill or be kill-stolen. It is entirely possible to "tag" every guard and get every meaty experience point, while the other players get naught. Then, it too polarized a preexisting issue: competitive combat/kill-stealing (which, at least in my opinion, had been relatively benign back then).
Yes, I cannot deny that the action bar has made combat more dynamic. But has it also made it more arduous to train? How many players can coexist in a mosh pit of hobgoblins (or whatever the new fancy killzone is)? Is the grind shorter, or longer?
These problems are probably hypothetical at best (eg. they're all in my head, man), but if Runescape's community has taught me anything, it's to be efficient. That can and probably will be a tough bridge to cross.
P.S. The ideas stated here may not be the most eloquently stated, and some ideas may have been lost in the process.
Edited by Reluctance, 27 November 2012 - 11:12 AM.