Before Cataclysm came out the archaeology system was one of the features that I was most looking forward to in the expansion. However, once it came out, due what I heard and read about it in various places, I rapidly lost interest. For example, in a video guide to the system here the guide spends roughly half his time whining about how boring the system is, and how it seems designed to get lowbies ganked. I finally got around to trying archaeology last night, and found myself pleasantly surprised by it. Rock bottom expectations going in to something will do that for you I suppose ;-)
I like the little lore tidbits that you can unlock. I like that it doesn't take up precious inventory space. I was also surprised by how much XP you get from it. At level 77, with rested XP I was getting 30,000 XP per area I cleared out, and 15K once I ran out of rested XP. That's pretty good considering a typical even con quest turn in is about 20K XP at my level.
Further, I think it adds something the game badly needed: a rewarding solo activity for when you don't feel like questing or grinding on mobs. Fishing could have been that system, but I dislike how long it takes to advance it at higher levels and how fickle the random advancement system can be. Cooking could have also been that system, but every time I've taken it up I've eventually abandoned it due to the enormous amount of storage space needed to keep ingredients stocked and the stochastic way that you tend to acquire ingredients (and thus are able to make food). I don't want to carry around randomly sized stacks of six different types of food in my bags at all times. Finally, neither of them yields XP on par with questing (if admittedly a good bit slower once you burn through your rested XP).
The system isn't perfect. I'm not really looking forward to making the same 5 silver vendor trash dwarf boot multiple times. I'm also never quite sure which dig sites belong to which race on the big map (perhaps I'm missing something). Lastly, a flying mount is nearly mandatory to make decent progress, and I'd honestly recommend waiting on the epic 280% flyer to get started on it.
However, all in all I had fun with it. I made decent XP without getting into a single fight (well apart from random gray mobs that committed suicide by attacking me), I had a good excuse to fly around the old world picking up flight paths I missed my first time through, and I also made a decent amount of cash mining as I flew around. I won't be doing it every night, but for me it will be a nice change of pace from questing now and again.