It can get a little busy at times (especially Wednesday afternoons!). Time your workouts around this and it shouldn't be a problem. There's also a special weights section for members of Gryphons societies, I think (I should really use this but I've never found the time to get an induction).
To be honest there are bigger and more functional gyms about, but you can't beat it for convenience, and it's got a good atmosphere in general. The staff are also pretty friendly too, which is also a bonus. Whatever the case I've stayed there for the past 3 years, and have no intention of changing.
You may also get a free membership if you're in halls, although I'm not sure if they still do this.
Summary: I like it. But make sure you know what times to avoid.