I too just bought the GMC Denali. As a Grad Student, this bike was really the best I could afford. Also, I figured it's better to start riding and outgrow a bike rather not ride while I save up for something to grow into.

Assembly was easy out of the box. Tightening the handlebars was a trick. I had to stick the long end of the allen wrench into the post and try to turn the small end with a separate wrench. Tricky, but it worked. I also had to make slight adjustments to the brakes. And spent a lot of time centering the front wheel. All told, it took about 2 hours but I have no experience putting bikes together. Someone with the right tools and experience could probably whip it together in quite a bit less time.

Everything is probably broken in by now. I've been riding a week now and have gone about 54 miles. I need to take it to my LBS to tune the derailleurs because I'm not comfortable doing that myself.

Personally, I hate the placement of the shifters. I'd like to replace the entire drop bar assembly and switch to an integrated shifter/brake system. My longest ride was today, when I rode around town and on the bike path we have here. I went 19 miles and the seat is a little uncomfortable. Then again, I have yet to get bike shorts. I'm hoping to buy some later this week and I think that will go a long way to reduce any discomfort.

Like you, I don't think the gears are big enough. I'm not sure if I should replace the crankset or the cassette. It's mostly flat here and, unless I'm riding in traffic (where I have to make stops at many red lights), I'm riding in the biggest gear.

I really do think that for the money this is the best bike around. I spent $150 at Amazon. So far I'm having fun and feeling great. Sure, it's not the last bike I'll ever own. But, it's a great machine to start out on. And, at least I'm riding while I wait to get something better!