A rating of 2.5 for a 9-holer is good, in my opinion. By far the best part about these nine holes (and what earned the rating I gave it) are the 27 concrete tees and the options they offer. Sometimes there aren't big differences between them (redundant lines), some tees are hard to find if you haven't played the course several times, and some are kind of getting eaten and hidden by tangles of trees and bushes. Regardless, the 27 tees allow you to pick your favorites and have a satisfying quick round (or multiple rounds).
Bandemer Park isn't a spectacular course, there's no wow factor, and the holes aren't very diverse, but it has great equipment and it's in OK shape. The fairways themselves are mostly clear anyway. It's not a "hidden gem". It isn't a course I recommend traveling to play, but might be worth adding if you are playing an area course, coming into downtown AA to eat some sushi at Totoro, and have extra time to kill. It just seems convenient for Ann Arbor. Definitely play it if you're in AA and need to get your disc golf fix but don't want to drive to one of the many spectacular nearby courses (this was the case for me and my wife).
The 9 holes play very quick and they're not very challenging, but keep in mind the course is out of the way of everything and somewhat secluded. Playing alone probably isn't dangerous, but based on what I saw when I played it, it would be a good idea to bring a friend or at least be prepared. It was really nice to have a spotter on a couple holes anyway, since the rough definitely has the potential to eat discs and there are several holes with blind pin placement. Oh, and leave your drivers at home (unless you might use one as a weapon).
I don't live in Ann Arbor anymore, but if I did, would I rather play Bandemer to get my disc golf fix, or drive 15-20 minutes (if traffic is good) to one of the nearby awesome 18+ holers? I don't know. I might just take a portable basket to the Arb with friends
In all seriousness, Bandemer is a great resource for disc golf in the area and definitely serves a noble purpose. Good people have been involved with the course and I give them kudos for installing and maintaining it in such a tangled mess. That being said, in its current condition, 2.5 is the fairest and most honest assessment I can give Bandemer.