My personal opinion on the matter is no. Don't get me wrong though, he is a strong pick that is one of the best junglers at peeling late game while also having a very powerful early and even a powerful mid with his ultimate that allows for either picks or just to disrupt the enemy team during a fight. This makes him a great choice for the lCS, but not so much your average solo que player. Here's why:
Gragas is not an easy champion to play in the slightest, regardless of what others think. His ultimate is actually quite hard to use correctly especially if they have a form of mobility, which if you don't time or predict can end up helping the enemy team more than hurting them. Pretty much everything in his kit is actually a skill shot, although q and e are quite easy to land.
His damage falls off pretty hard late game, which makes you almost only useful for peeling or catching people out with your bodyslam and ultimate. After the recently nerf to his W (I think it was this patch, or last, or maybe it will be the next) his damage late game will be almost non-existent. There aren't many people you can duel as a Gragas, meaning you have to rely on your team to do that for you, following up while you peel for them.
Basically, riot has adamantly been nerfing Gragas because hes playing almost every game in the lcs and until people quit playing him entirely, that probably won't stop. This means that if you buy this champion, he'll probably end up being a weak pick in a couple of patches. This is just how Riot does things, nerf, nerf, nerf until they are so weak they aren't seeing play for awhile. On the opposite of the spectrum some champions are buffed in this way, which is even worse.
Don't get me wrong though, Gragas is a good champion, not bad at all, but you are taking a risk buying him. Any champion can work, but not every champion can work as well as the next. For example, adc Leblanc may work in a game, but that doesn't mean it's GOOD, compared to all the other real adcs.
He is a fun champ to play (imo) so if you buy him I don't think you can go wrong if you take the game as what it's supposed to be, unless your in the lcs, and that is to have fun.