Eurodollars are very, very liquid. HFT's are definitely not the issue here.
Eurodollars are all about the Fed. Also, LIBOR needs to be taken into account. The Eurodollars are a lot of fun to trade, but can be pretty long-term positions (unless you just want to day trade and you like this particular market).
I traded Eurodollars for the first 6 years of my career, and I like trading them.
If interested, please call or email me and I can definitely help point you in the right direction.
I run an IB and a CTA and can definitely help you if you're interested.
Mike