I started out with RM2 and played that for many years. When RMSS came out we eventually switched over and played that for a long while but I never liked it as much as RM2. I think my main concern with RMSS was that it was too detailed, it hampered game play. IMHO it's more fun to have somewhat less skills that you can have a broader use for, it also allows for more inventiveness. But hey, that's just my opinion...
Having spent some time here on the board reading people's reactions and thoughts on RMU I feel a little lonely I must admit. I actually really like the Beta 2. It has something that I've never experienced in RM before, cohesiveness.
It seems no one is happy, both RM2 players and RMSS players complain equally. Maybe the complaints are different to each other but no one seems to actually like anything. I wonder if people are just being set in their ways?
The only thing that I have a problem with is backwards compatibility. If you change how many hit points monsters have and make it relative, it'll just be a big mess to use old campaign material.
Everything else I could totally live with and enjoy. I'd be happy to change over to RMU using the Beta 2 rules after they have been fine tuned for final release. In many ways I felt that the authors had solved things in brilliant ways even if it was done very differently compared to past editions. I still feel it holds true to the Rolemaster heritage.
I could keep playing RM2/RMC too, I'd be fine with that, but IMHO RMU is a great product. I hope they don't revert back in too many ways with the next beta, being new isn't a bad thing, it's just different.