So I own both GnR and Ultraman
I will add that I just got the Ultraman today so that makes me an expert on it (j/K)
I find them both to be the nicest looking games in my collection.
For GnR, I always liked the band but I find I like them more after I got this machine as I didn't really listen to Chinese Democracy and there are some songs on there that I like. I know there is debate about which Axel should be in the game but the old Axel vs the new Axel does not bother me (I am getting old myself). I definitely enjoy playing it but do find it heavy on multi-balls or at least 6 ball multi-balls which I struggle with as I seem to just hit another ball. I guess my main gripe with it would be the scoring, I have no idea how people put up these huge scores but all in all it is a good game and fun in my collection.
Obviously, like everyone else I bought UM before I played it. There was one at an arcade an hour or so away from me and I went to play and came back thinking OMG what did I just buy. I thought about selling it after that for a loss but then decided what the hell I will just get it and see how it goes and actually traded to move up and get it earlier. I got the UM today and actually think it will be good. As I was thinking about it today, it has a few things going against it when you play it for the first time in an arcade.
The first thing is the inserts are not marked (like where GZ will say "tank", "bridge", etc.) I think this is tough on understanding the rules but does leave them open ended to be coded to do many things as they develop the game.
Second is the game is a little different and it kind of messes with my brain but as I played it I was getting the hang of it. Two things that get me are the ball lifters and using the flippers from the top to the middle playfield. After a few games I was already getting the feel of the ball lifters. As for the flippers the top flipper is the right button and the middle flipper is the left button. I just couldn't get it in my brain to press the left button when the ball drops down but I am coming around now.
The game has some good shots and flow with the upper ramp but also has a few harder shots with the right orbit and lower Baltan scoop. It has a bunch of modes which seem fun so far.
I think most people that are buying it at a discount will probably be happy when all said and done. People beat up UM more than HWN but they are basically the same game. My advice would be to hold on to it (instead of taking a loss) and see how it goes.