Is this desktop worth $620? Did I get an amazing deal?

I don't Know!

It's not an amazing deal. It has A LOT of RAM but that's meaningless because you're not going to do much at all with dedicated graphics and just an alright processor.

Install a GPU yourself - get at least an AMD 7850 or better - then you'll have a very nice computer.

You won't be making use of that RAM lol, should send it over to me… Hehe.

Seriously.

To answer your question:

I wouldn't say you got a TERRIBLE deal, but it all depends on your uses. If you're a gamer, it will pass so long as you get a good graphics card. In that case it was an ALRIGHT deal and I wouldn't say you got ripped off or anything. You likely won't be making use of all of the RAM, ever, though, especially with that i5.