Anything made/assembled by Century should be looked at very closely. A few things I know to watch out for specifically with the CETME:
1) Make sure the triple frame is straight. If it's not, your gun won't shoot straight. If it's too far out of alignment, the cocking tube will be so far out of whack you may even have trouble cycling the gun.
2) Make sure the barrel, trunnion and receiver are put together straight. If not, you may have excessive wear on one side of the bolt, and if it's too far out of alignment, it may cause an issue where the bolt doesn't lock fully into place.
3) Make sure the muzzle brake is put on straight. If not, bullets can hit the muzzle brake on the way out of the barrel, causing shots to fly off of target. If this is an issue, you can have the opening on the brake opened up some.
4) Make sure the angry monkeys at Century didn't grind the bolt. Head space on these rifles is measured by the gap between the back of the bolt and the front of the bolt carrier (look up the magazine well with the magazine out and the bolt closed, you'll see the gap I'm talking about). If head space is not right, the correct way to fix it is to change the rollers to give the correct head space measurement (they make oversized rollers in a couple of sizes). The way Century "fixed" it in many cases was to grind the back of the bolt head until they got the head space measurement they were looking for. Not only is this the wrong way to fix this, but it can leave you with excessive headspace.
As torpedoman pointed out, the CETME design was licensed and copied by H&K for the G3 rifle.
As for whether or not they're worth the investment, it's your money, so who are we to say? They are loud, they have fluted chambers (hard on brass if you reload), magazines can be an issue (some will take all CETME mags, some will take G3 mags, some are finicky about what mags they'll take), and they throw brass a long way. On the plus side, they don't kick much, they're easy to handle, and they're fun to shoot.
I don't personally care for the ergonomics of them, but I think I might be the only one.