1) If you have an HD TV set (it should be marked 1080p and not just HD-Ready), blueray is certainly worth it (as Duffman already pointed out)
2) A basic blueray player just reads digital recording and sends it to the TV. If this is the only thing you want to do, there will be little difference between players
3) If you want to use it for DVDs to, check how good "upscaling" is. The difference between a basic and good player is massive
4) Blueray disks carry a lot of interactive content and "loading" a disk (from the moment you insert the disk till the moment you can play it) can be substantial, up to a few minutes. A powerhouse, such as PS3, wins
5) If you have a good sound system, triple-check that it performes well when supplied with a digital (as opposed to componenet analogue) signal. If you need a blueraqy player to provide analogue sound, you will have to pay substantially more... up to 3 times more if you wnat the sound to match the quality of a high-end CD player
6) Like any computers, blueray players come with bugs in software. Some of more expensive models can download software updates via internet. Updates can improve the experience with a particular player dramatically
7) If you expect to play DVDs it is worth considering a multirigion player. No player will play blueray disks from all regions but some will play DVDs from any region.