Sorry so long - my rambling thoughts and experiences on this
**Standard Disclaimer. This is my opinion.**
I have several thoughts on this.
I really like the Alternity system but it has been OOP for a while. Four years ago, my players indulged me and we played it as a Fantasy setting, using rules found on the Alternity site. The first campaign we tried worked mostly well. Then I started making my own rules. They worked okay but I had gained a rules lawyer player and he showed how they worked most of the time but there were big holes at the extremes.
So, over the next two years, we tinkered. We tried things. We looked for other rules. However, in the end, I was the one pushing it forward. So, I had to write rules, playtest them as best I could, present them to the players and run the games. I had to do everything. I knew this, so I am not mad at my players, but when I realized that, it was too much work. So, we stopped the Fantasy campaign using Alternity.
We did play a Modern game with it but after one campaign, I felt like we knew the system and had pushed it as far as it could go. As much as I do like the system and many of its ideas, I wanted a more heroic system than realistic.
Looking back, this showed that trying to use a system for something it wasn't designed didn't work very well. There was little support online as well and responses weren't fast. That combined to make it tough, for me and my group, to use it. We also found out that once we had played a lot of the options, it started to feel the same to us. We had fun while we did use it but it couldn't sustain itself for us in the long term.
There is another aspect to this. Alternity was a newer system, compared to DND another game we play, and so I enjoyed the new game theory that was in it. (I don't want to get into lots of details here but it had a different style than DND.) It was different and in a way that nearly matched what I wanted in a game.
Now, having said that, there are some OOP system that I haven't played and would try, such as oWoD, and it has enough material for years. However, there is more to it than just the new material.
At the same time all of this is happening, DND 3E had gotten old to me. I was ready to quit 2E and find an alternative, when 3E came out and energized me. But, within a few years, 3E was already showing me how it didn't work and had the same problems I didn't like with older editions. However, I did like the fluff of the books at the time. Further, the designers were trying something new and the theory of gaming was advancing and I appreciated those.
When 4E came out, I have completely embraced it. Before, when reading a new non DND system, I would think "wow, I wish DND did that as that's cool." Now, I think "wow, 4E handles this much better and this system could learn from 4E." It's a very big change for me that, after twenty years of hoping DND would do X or Y better that it finally does for me! I am enjoying that a lot. Further, I really like the game theory that 4E uses. The ideas on the DMG2 about vignettes, for example, are awesome and something I would take to other systems. (In fact, I am surprised White Wolf hasn't already published rules and ideas like that. I think those ideas have only appeared in one other published work, but I am not sure of that.)
So, what does this have to do with OOP? Well, I don't think I could play 1E/2E at this point without it being so modified that it's not that game anymore. Even though there is a lot of of stuff out there, 1E/2E doesn't work for me as a game. I'm a firm believer that role playing is influenced by the rules you are playing and I don't like 1E/2E and how it works for all levels but about 5-8. 3E works better but plays differently based on what level the characters are and again breaks down as 1E/2E does even if it is later levels.
tl;dr : So, could I play an OOP game? If it fits my style and the style of my group, yes. I don't know how long it would last but once the system was explored, I think it would be tough to keep playing it. That's why I like 4E so much because it has so much more variety (a dwarf fighter is not the same as a human fighter as they were before) and a lot more to explore. Playing the game is as much about exploring what the rules can do for the game as it is about the story we are telling.
That's just my opinion.
edg