They used to be solid, just big and heavy. But like all things HP, I wouldn't touch a current generation model. I'm sure they've been cost optimized and are just a Taiwanese product with an HP logo and price.
I'm not familiar with the 3650, only the 3550 and 3750. The 3750 are decent switches, also check out the Extreme Summit 48si and the equivalent Foundry switch. If you don't need the L3 capability, consider the Dell switches, though they just replaced their nice proven 3348 switches with a totally new architecture 3448 switch with *no EOS notice to customers*, thus demonstrating Dell's cluelessness about the enterprise market. SMC and D-Link are also worth considering for L2-only stackable switches.