Been to Langkawi twice while travelling to and from Australia. I loved it but it's very quiet. Definitely not the type of place to go for mad partying, happy hour etc. In saying that maybe the hotels have entertainment in them. I know there was an Irish bar in Pantai Cenang which was no more of an Irish bar! I went into it one night and had a pretty good night. Mainly locals and ex-pats drinking in it. Also there was a great restaurant called Champor Champor that had a little bar in it. We went in one night thinking it would be just a meal with wine and ended up drinking the night away with a few English couples and a local musician! I'd go back again but like I said, give it a miss if you're ideal holiday is the canaries.
PS Was there in 2001 and 2002 so can't speak for it now. Check out the forum on Trip Advisor and you might get some recent info.