A good tent definitely is something that will last you and will make camping more comfortable than some cheapo thing.
Let's see... some features of my tent:
I love having a gear loft (basically a netting that clips at the peak so you can put gear in it overnight.
I like the tents that don't have the cheap tarp material in the bottom. My good tent is all the same fabric.
I like tents with a full coverage, fully waterproof rain fly. I hate tents that just have a tiny little rain fly and leaves the actual tent to fend off water. That's what the rainfly is for.
Its nice if the rainfly rolls up, too.
I like having a decent vestibule in the rain fly to store stuff that doesn't need to be in the tent with me/us.
Aluminum poles that fit flush are great, versus those that have cylinders around the fitment points that stick out and catch on the tent as you're threading it through.
Mine is a two pole so it is crazy simple to set up. I would rather have a tent that is simple to set up-- a hex shape with 3 poles, for example, rather than some weird igloo looking thing with poles at weird angles everywhere.
A tent with a matching ground tarp is great -- too big and it lets water go under the tent. Too small and, well, it doesn't keep the tent from getting dirty & abraded by ground.
My tent and rain fly have excellent tie downs that keep the tent staked down in high wind but also keep the rain fly away from the tent proper to keep water/moisture off it.
For size... I like to use a 4-person for two people (my cheap tent which I'm not super fond of but it does ok and it was free so who am I to complain) and a 2 person for just me. That gives me room for backpack and other gear. But the 2-person has slept me and my wife before... and it works... but that's why we got the 4-person
