Normally I tend to write a lot... but I'm going to try and simply touch on my overall thought on the various versions and how the fans behave in their preference of them. There there are definitely specific parts of RMU I highly dislike, I want to cover broadly rather than get into specifics here.
There are things I like about RMU compared to RMSS and things I don't like. Now, there is a balance of one over the other that sways more towards RMSS in general, however if that were not the case there's still a serious issue that I think needs to be overcome for RMU to pull the RM2 and RMSS users in in the numbers desired and that is...
RM is, I think most of us will agree, traditionally a veterans game and started as a piecemeal system that you assembled to fit your tastes. While it evolved so did the users, creating their own version of RM. If they didn't like something they used one of the published options or created their own material/rules/design. So a lot of people that started with RM2 didn't really NEED to move to RMSS. We had used RM1/RM2 material to modify D&D over the years, moved from D&D to MERP, then when RMSS was just coming out we decided to go to RM fully. We looked at both systems and saw that RMSS was going to be easier to learn as a full system as RM2 was scattered and bloated (and unbalanced in some cases). From that point we then went through the same evolution that RM1/RM2 players did, if to a slightly lesser degree because RMSS was not so piecemeal. But in the end we find ourselves in the same position RM1/RM2 users did when RMSS came out. Is there a enough good reason for us to buy into the new version?
Let's just say I liked 50% of RMSS and I like 50% of RMU. I've fixed the 50% of RMSS I didn't like. RMU now has to not only meet my version of RMSS, it has to improve upon it. It has to do that for all its target demographic and its target demographic all have different ideas of what the 'perfect' system is like... so you can't possibly accomplish that goal. This is why RM lost a lot of its users going from RM2 to RMSS and why I think it will lose a lot of RMSS users in going to RMU. The first post in this thread is a good look at how one, of many different possible players styles, viewpoint is going to compare the versions. The basic comparison, then the comparison of how they've modified their own version. I think if RM intends to become a product capable of supporting a true company it needs to forget about the old customers and focus on new ones and RMU, in my opinion, does NOT do that. Of course, then we get into if that's even possible these days... but I digress.