It tends to be a bit below BETA SP in quality, mainly because of its composite nature. The video image was 'downmixed' to composite before recording onto the disc. This gives all the tradtional problems that composite video brings. If it was kept in YUV before recording, it would have been a cleaner format, but as it is, it is still the best of the analogue formats available to the home consumer. So if you fed a betacam SP deck a composite signal, the quality of it vs LD would be pretty close.
So its much better than betamax or VHS, but nowhere near as good as DVD.
Also, the SN ratio on a lot of players (especially Sony) was poor, so the player makes a HUGE difference to the quality of the image you get from a laserdisc.

Now of course you can find laserdiscs that look great and DVDs that look crappy, but the best laserdisc transfer doesn't look as good as the best DVD transfers by quite a margin. Also, the transfers were often of a lower quality than they are today due partly to consumers not being picky enough (i.e. When comparing to VHS, even an average LD transfer looked good), and partly due to the telecine technology advances in recent years. You could probably prooduce a much better laserdisc today than in the 90s.

Often Laserdiscs have a better 5.1 surround track than the DVD release of the same movie. This isn't anything to do with the laserdisc format itself, but more that many DVDs have a compromised 5.1 soundtrack - they remixed it so it would still sound good when played in mono or stereo. The LD 5.1 soundtracks were only intended for 5.1 so sometimes you get a much bettr S/T on the laserdisc version of the movie (HEAT is a good example, the sound is outrageously better on the LD) But when the 5.1 mix is the same on the LD and the DVD, they sound identical.