Some changes made to each R&C followup have been of a more lateral variety, intended just to mix things up rather than to improve the overall formula. Meanwhile I do think they have incrementally improved the core elements of the series with each game and this game in particular. They've tightened control, added additional control schemes, improved the context sensitivity of certain actions, deepened the Quick Select. They've taken a survival of the fittest approach to the weapons and gadgets that have been aired so far, eliminating some, tweaking/streamlining others and even converging a few. The storytelling and characterizations on offer in UYA are the best in the series so far.
The level design is perhaps the most divergent in that it moves the focus away from larger and larger monolithic levels in favor of more and generally smaller levels with a greater focus on skirmish type encounters. However, I don't see any significant decrease in the amount of platforming involved. It's got about the same focus as its had throughout the series so far, and there's at least a few levels in the game where the focus is mostly on platforming (Obani moons). I find the aesthetics of the level design to again be the best of the series because, while the levels retain the now familiar R&C blend of retro-scifi styling with Saturday morning cartoon character designs, they've managed to pepper the homogeneity of this look with a few more otherworldly setpieces than we've seen thus far in the series. The overall presentation of the game's levels are further enhanced by the smart use of bloom/glow effects, better water effects and a much greater use of specular highlighting.
On top of all that, you've got the online component. It doesn't go about reinventing anything but it nails the execution almost flawlessly. Hosts and players have got just about every option they could want to start and find games, create buddy lists and clans, all within a very accessible and largely intuitive UI. The gameplay itself is surprisingly indistinguishable from offline gameplay in terms of performance for me thus far. The game types are familiar, but the use of trademark elements of R&C gameplay help them to stand apart with the particular mix of weapons (like the mine layer and lava gun), the light acrobatics, the gravity defying antics of wall and ceiling walking and the use of the swingshot and dash boots.
Not to say I don't miss some aspects of the earlier games, but the overall change has been positive with each release for me.