I've done a couple of stays here when catching the SQ 7 AM flight to Singapore. Never stayed in a US HP but the hotel is fine just a normal generic entry/midrange hotel. The HP out at Scoresby is better but a long, long way away. EF will normally upgrade, although most rooms are the same just with different views. The twin Queen is the highest category of room and differs from the others in size and having a bath.

I have my own car so have never used the shuttle. Just be aware if you use a taxi/uber there's a good chance you will get a grumpy driver as they hate the short fare down the freeway to Essendon - however that is their problem and not yours.