New terminal at Colombo is definitely a huge improvement over the previous offering, but still not ideal for long stopovers. If you have enough time (and as some other posters have suggested) take a break at one of the hotels in the vicinity. I usually stay at Tamarind Tree, just 10 minutes away and a wonderful colonial-style resort. Rooms are grouped in twos or threes in individual bungalows, with a swimming pool in centre of grounds. Good bar, too.
As for UL, I use them frequently and whilst never a disaster, I find their offerings rather dependent upon cabin crew. Seat pitch and comfort OK even in Y class. Food: I have often wondered whether anybody in their flight kitchen knows how to cook anything (really: anything) else other than saffron rice with rubbery lamb (or is it mutton/camel/donkey)? Drinks: beer or wine not always volunteered, but forthcoming if you ask for it.