Damn, I feel trolled. I start a topic for Slowbro only for this ancient one to be bummed up. Whatevs. Here's my main points from my Slowbro topic:
So, what's up with Slowbro? For quite a long while, Slowbro has been  outclassed by other bulky  waters and cursed with a terrible pursuit  weakness. He was the perfect  Machamp counter last gen, sure, but Hypno  is the perfect Breloom  counter, and that didn't help his usage out very  much. Regeneration and  boiling water are just huge boons to him.  Seriously, look at this guy:
1)  Myriad of support options. Yawn, Thunderwave, Toxic, Boiling Water,   Rain Dance, Trick Room, Light Screen, Safeguard, Disable, and even   Healing Beam for doubles. Some of these are more viable than others, but   the Bro certainly has plenty of options.
2) Regeneration. As  mentioned above, this is huge. His pursuit weakness  is also mitigated  when combined with this. Check out the calcs for  252/ 252 Bold Slowbro:
Adamant 252 Tyranitar's pursuit: 200 - 236 / 50.8% - 59.9% 
CB Adamant 252 Scizor's pursuit: 194 - 230 / 49.2% - 58.4% 
Adamant 252 Honchkrow's pursuit: 188 - 224 / 47.7% - 56.9%
Do  I really need to go on? These are all hitting at about half health,  but  when regeneration comes into play, the damage is easily solved. I believe these are right, but you're welcome to double check. I used Metalkid's calculator.
3) Instant recovery. One of the most important things for a wall is gifted to Slowbro via Slack Off. 
4)  Decent special attack with a huge movepool. A base 100 attacking  stat  doesn't exactly strike terror into the opposing teams, especially  if it  isn't boosted, but it can get the job done quite well. He can  even learn  fire blast and flamethrower to roast steels. One can even  opt for a  gimmicky specs set with regeneration. 
5) Slow as crap. This is  actually an advantage this gen, as Roopushin  can't hit Slowbro with a  max power payback. Slowbro can also hit Roo  quite hard with STAB  psychic. 
6) Quite a few options for boosting. Slowking has it  beat thanks to  nasty plot, but it can learn amnesia, curse, and calm  mind. Boosting  doesn't exactly mesh well with regeneration, but it  remains an option.  Amnesia, for instance, can greatly increase Slowbro's  survivability.