They are some serious differences physics wise.
The first Climax game I played was 06 on the 360. And I loved it. Then I went back and played previous iterations, 2 was b/c. It was fun, but I enjoyed 06 and 07 more.
07 was fantastic. 60fps, better cockpit views, and I actually enjoyed the career and extreme modes.
My favorite last gen though was 08. I just preferred Milestone's physics and cockpit views. You couldn't tap the rear brake to powerslide around which I know people loved.
Monumental did a great job with 10/11 too. Another one at 60fps, with great graphics and large grids across the classes.
I also played all of the SBK games that were released in NA or region free to import.
15 keeps a lot of the same Milestone physics as their previous MotoGP and SBK games. They did make it a bit tougher on Pro physics, you can easily lose it simply from changing from first to second gear from the bike stepping out.
They finally improved the graphics to make them closer to a next gen release, Milestone games have always been lacking in graphics, mostly the trackside details and lighting effects. Bike and rider models and animations have been typically been really good though.
Not too shabby-
15 has a huge bike list, the full 2015 and 2014 MotoGP, Moto2, and Moto3 rosters. They also have a Redbull Rookies cup class as DLC, and historic packs including 4 stroke and 2 stroke bikes and riders. IMO, it's one of the best MotoGP games yet.
RIDE is fun, but really lacking in graphics for a next gen game. Super long load times too. But it has a great street and SBK type bike list. 15 tracks with multiple ribbons and you can customize your bikes and rider too. It's the only place to race Imola and Road America on a bike this gen.
Playing the same bikes between DC and RIDE is really jarring. It's amazing how good DC's bikes look.
So, long answer to your question and a unplanned rundown of bike games this gen I guess.
I played MotoGP 14 the most of any racer this gen so far. Went through the main tour of DC but a ton of DLC to finish. And I just don't have the time yet to play more 15 and pCARS.
Between MotoGP15, pCARS, WRC 5, and DC, I'm set for racing games for a long time.