A lot of the mexican (or tex mexican) I had in CA was over salty, over cheesy and definitely over stodgy. But I had great stuff too, huge fresh burritos full of vegies and pico de gallo and the meat or beans was perfect and not some congealed lump. So I know what relayer is talking about, I haven't been in the UK in a long time but I'd be very surprised if you could get good mexican. It's easy to make yourself though and to avoid the whole taco bell style slop.
I would say 4 out of 5 meals I ate during my upbringing contained beans, mostly garbanzo. I can't really get excited about garbanzos for that reason though I do love crushing them to death with garlic and lemon..