As a former pontoon boat owner.....
They are under-rated fishing vessels. They can go very shallow, can be beached without harm, can fish 3-4 people comfortably, and provide a level of luxury that most vessels can't. They're cheap (you can get a decent one under $5k used), plentiful, and can support 10 people for playing around. No problem tubing or knee boarding behind them (he had a 70hp on ours), but watersking is so-so, and wakeboarding is probably out.
On the down side, they are prone to catching wind, you're not going to go much over 25 mph in most pontoons (exceptions exist, of course), they sit a bit high in the water (low bridge issue), and IMO, they're a bit harder to trailer, especially in side current (river)... It's just harder getting two toons to line up than it is to get a conventional hull centered.
They are not well suited for rough water/high waves.
Still, if you're looking for a good, cheap way to go fishing and still be able to take a half dozen friends out playing around, they might be a good choice for you.