I got it on the second generation but part of me wishes I took a little longer to get more stuff. The upgrades are interesting, and while I don't think I could play long enough to get full upgrades, it was a nice touch to have. I would like to see shield movements incorporated more into the gameplay, because it was a really good move to have the enemy shield movements as something you had to avoid.
The only thing I noticed is that the horse upgrade didn't really make me go any faster. I'm sure that'd be more profound at higher levels, but that sort of makes it worthless to buy the first two upgrades for horses (as far as I got) because they capped at 18 mph.
Still, though, overall it is a fun game and a good time sink.