Cartel is a Tempe classic. I've been going here since I was in high school, and it honestly hasn't changed much at all. It's a super hipster coffee shop with an industrial interior. It's certainly a hot spot for people to do homework and catch up on work, so good luck finding a spot to sit when you go!
Personally, I love to get a dirty chai, which is a chai latte with a couple shots of espresso added. The flavor is amazing and the texture is creamy and delicious, but it still gives you that kick of energy from the espresso. Coffee is really an art at cartel, and you can taste the difference.
It is a little pricey, but then again, it's an art. You definitely pay for the love that they put into your drink. Sometimes the people that work there can be a little snobby about the coffee - friends I know that aren't super into coffee and prefer PSL's from starbucks have been a little put off by the customer service there. However, that's not always the case and the last time I went I was very impressed with the customer service and how helpful the guy at the register was to my non-coffee drinking friend.
All in all, Cartel is a solid coffee shop with delicious coffee and tea. Try doing some homework there one afternoon and enjoy the atmosphere!