In the last two months I've climbed in somewhere around six different gyms due to the travel schedule. I actually really like climbing on plastic and always have. I generally get my ass kicked, but that's what's so good about it--on rock I can often trick my way through difficult moves, but plastic strips climbing movement down to its most basic form. Back in the sixties my parents used to joke that one day you would be able to buy hand holds in the climbing stores, their joke is now a fun reality.
I've honestly enjoyed every gym I've climbed in over the last few months, and have some decent fitness going at the moment thanks to the plastic abuse. Paragliding season normaly leaves me a bit, as my my friend John Winsor says, "Fat and sassy!" but this year the comps have been near good climbing gyms so I've at least avoided the fat part. Good gyms share a few features. First is a motivated local scene. We've all seen the forlorn climbing walls inside health clubs, abandoned by the clientele and largely ignored. Some gyms inside health clubs, such as Chelsea Piers in NYC, thrive thanks to the local scene. Chelsea has a monster over-hanging wall and a good manager (Les), plus a crew of motivated locals, so it's going well. The bouldering needs work at Chelsea, but it' the most entertaining roped climbing I've done in a gym of late.
Height isn't everything--the Vsion, in Canmore, is short like a pygmie but has the best bouldering of any of the gyms I've climbed in lately. There is no excuse to walk out of that gym without blasted fingers and arms.
Good gyms also use a comprehensible system to mark holds. My biggest complaint in any gym is a poor hold marking system. This is going to be a controversial statement, but after climbing in dozens of gyms all over the world I'm going to make it: Plain old colored tape is WAY better for marking holds than using holds of the same color, putting colored doo-dads on the bolt heads or any of the other schemes I've seen (putting colored pieces of plastic behind the holds so that they stick out is second best in the marking scheme rankings). The colored hold idea sounds great when presented with a box of new bright red holds, but the reality is that using colored holds to set routes limits the creativity of the route setter (there are only so many types of hold per colored set), the number of routes that can go on the wall, and confuses the hell out of climbers. Those bright red holds start to look a lot like the bright orange ones after a few years of thousands of chalky hands grabbing 'em. I spent the last week climbing at a great gym in Montreal (Allez Up!), which has all the requirements of a good gym (great local scene, good staff, good routes, good bouldering) but suffers from using colored holds. I often heard even local climbers arguing about whether or not a hold was "on" the route, that's just frustrating for the climbers in the gym.
The floor system of a gym is also important, especially for bouldering. My favorite is the huge thick track and field crash pads found in gyms such as Allez-Up and the Calgary Climbing Centre. You can pitch off from even 15 feet up and relax. Second best is thick padded carpet with mobile crash pads, such as is found in the Wall Crawler gym in Atlanta, the Rogue Rock Gym and the Vsion. The problem with mobile crash pads is that you have to move them around, and landing on the edge of a pad can result in a twisted ankle. Pea-sized gravel is actually excellent for crashing into while bouldering and for protecting lead plummets, but turns the air into an Asthma-inducing miasma of chalk dust, gravel dust and who knows what else. Cut-up tires are a nice bit of a recylcing, but the chalk dust tends to settle into the tires and get disturbed each time someone falls on the tires. I also shudder to think what those tire bits are releasing into the gym air.
Health-club style fitness equipment is generally a waste in a gym. Nothing makes you climb better than climbing, and most of the time the bench press in a climbing gym is relegated to holding climbing bags or as a good place to sit between sessions on a boulder problem. Get rid of it. A good pull-up bar and a campus board is about all it takes, but many gyms don't have a decent pull up bar for working on front levers or just doing pullups.
The staff also counts in a gym; I'd rather have a relatively average climber who checks my belaying skills out and is friendly than a local rock star who can't be bothered to be friendly to everyone. I've seldom had a bad experience with staff in a climbing gym; occasionally someone will recognize me, but often I go through the check-out procedure just like everyone else, and that's cool with me. I heard through the grapevine that John Bachar once failed the belay test at a gym in San Francisco, I'm always a bit nervous about whether or not I've using my ATC in the locally approved manner. Standards vary. Good gyms tend to recognize that lead belaying requires a dynamic response from the belayer, but some gyms still insist on tying the belayer down. That's OK for top-roping with a fat dude and a small women, but not on a lead wall.
I've got some more opinions on climbing gyms, but time to get on a flight back home to Calgary, and the "I fly way too much so I get to sit in a nice chair and drink while I wait for my next flight" lounge is threatening to cut me off the good scotch.