Not amazing, buts its not terrible either. Its average. If you're looking for a single player experience, its not here.
First of all, once again, Breach is an average shooter. There's almost nothing different that hasn't been tried in other shooters, save for one game mode, convoy. This will be discussed later. The guns are the same. Maps don't stand out. Rank system sucks. Almost everything is average...or below.
Convoy is 2 teams, one escorts a 2 vehicle convoy, another tries to stop it. The convoy team has a time limit, which gets added to every time they reach a checkpoint on the path. Other game types include team death match, sole survivor (TDF with no re-spawning), Free for All, and another mode similar to Capture the Flag.
Breach may have promised to define interactive environments, but honestly, it's just a bit worse than Battlefield's.
The class system is also similar to BF's. They each have a name, and certain weapons. To upgrade these weapons, you must gain XP. To get new weapons, level up, using XP.
The maps are mediocre. None are very good, but some are bad.
The cover system is never seen in first person shooters, but very common in Third Person Shooters. so this part is unique about Breach. Here, you can hide behind almost anything, and can switch between shooting first or third person.
There is no campaign. The game may be 1.3 Gbs, but the only thing here is online multiplayer.
The audio isn't a big part of the game. The only noticeable sound are the gunshots. Almost no dialogue.
The graphics are acceptable. Doesn't stand out, but they're decent enough.
Gameplay is ok. At first, I lost interest, and left but after returning to the game, it was actually kind of fun.
Overall, I would recommend playing some other game. Breach is overpriced, so if you are planning on getting this, wait for a sale. But otherwise, get COD of BF. Much better use of money by far. If you already have those two games, stick to them. There's nothing here in Breach worth seeing for 1200 MS points...or however much it costs on the PC.