That's the thing with martial arts, it really depends what you want from it. As you can tell a lot of people will argue the effectiveness of a martial art as a means of self defence. Some martial arts are more sports in that you need to perfect technique, spar against someone using the same techniques and the like and you could argue that if you want to defend yourself they're not as suitable towards that end because they play according to strict rules and don't always cater to the idea of someone grabbing you or whatever else goes against the norm in sparring. However, it does depend on the dojo, style, martial art so it's certainly not simple. Then there are martial arts that employ techniques such as grappling, grabs etc which are more useful in self defence. I think there are 4 main aspects to a martial art; sport, self defence, fitness, fun. If self defence isn't so much of an issue you can still fight, practise a sport, get fit and have fun.
One specific I will go into is taekwondo. It's pretty much only kicking as far as I know and for a beginner that can be a bit off-putting. I've done a little karate recently which involves kicking but not as much and I can do front kicks easily; being 5'10 I can kick people in the chin or head who stand about 6'2 tall. However, switch to a roundhouse kick and it can be a lot more difficult on the hips to even get above midway up the torso, the stretching involved is no walk in the park. And then there are axe kicks, back kicks etc. If you're not put off then fine but just be aware you may have to be persistant when trying to make progress.