I dunno, I played PT a lot in Brawl, so 2.5 Squirtle felt horrible to me and I didn't end up playing him at all. 2.6 Squirtle, to me, feels exactly how I wanted him to transition over from Brawl. All of his momentum tricks, shell shift tricks, everything.
I know a lot of people here probably didn't play PT in Brawl, or played Brawl at all, but everything I learned in Brawl was easy to carry over to 2.6 Squirtle, so I guess the high learning curve he has was already over for me when I started. I just need to stop suiciding all the time.
Slingshot SHFFL's are not the only thing 2.6 Squirtle has at his disposal, though they are incredibly useful. Almost every time Waterfall could be used to KO, a sweet spot UAir can do the same thing, not to say I don't try to Waterfall when they're too high for a UAir myself, but yeah.
I almost never approach with Withdraw, honestly. I tend to approach with slingshot SHFFL's (really useful to learn, and not very difficult imo. You have the shell shift option, or the RAR option to get the momentum), Bubble (wavebouncing can mix it up and keep you safe) Water Gun can lead to grabs at low percents, crawl tilt if they are in that range (which is honestly the best thing they could've given him, it has armor, goes through or under projectiles, and pops them up for an easy combo even at lower percents), wavedash in or shell shift dsmash is huge, especially because it is + on shield, so you can either keep the pressure on after the attack, or it makes for an easy get away. Also he has tail invulnerability, so ftilt and dtilt are very useful for approaching as well, and can both be comboed out of at low-mid to high percents.
Rat gave me a tip for using Withdraw last night, though. It's good when you know your opponent will be throwing out attacks, because its so quick. The example he gave me was it's really good in the Ike MU. I need to find more uses for the attack though, I mainly use it to recover and to stop my momentum when pushed by attacks like Wolf's up B when botching a gimp. I don't feel like Squirtle even needs it to be a good character, but the more options, the better.
One last thing, I know they took the Withdraw jump turnaround out, but you can still turn around on the ground and jump while still in your shell. Obviously not as quick as before, but it's not technically removed from the game.