It is impossible to overstate how much of an upgrade the D gates are -- this was a grand slam home run move. Precheck, nicer facilities everywhere, much better food options (and open later for redeyes -- but still not late enough IMO). I usually hate trams but the LAS trams are well run and efficient and totally worth it to get to D gates. They also keep precheck open late which is huge (because they even close down first class line around 9 or 10 PM usually).