What Dan said. Abs are totally not worth worrying about - I've seen too many people get disappointed with not being able to have them, when they really shouldn't be.
Point to remember is, your abs are there - it's just whether you can see them or not behind your natural body fat. I know guys with much, much more core strength than me who don't have defined abs - their body type just isn't right. By contrast, I pretty much have good abs all the time, but I'm piss weak at the moment - I just have a relatively low amount of body fat. ("Ectomorphic," if you want to use the overly simplistic idea of somatotypes.)
If you want one thing that will make you look and appear healthier, it's (IMHO) great cardio fitness. Not being out of breath and overly sweaty when you do stuff is a Good Thing.