a) Average reliability - had numerous incidents at their London and Fremont DCs. And the complete inability to tell me what was happening in a timely manner was pretty unacceptable.
b) Average support - they will answer the simple questions very quickly. But anything reasonably complex they will actually not bother responding at all.
For me :-
* Excellent reliability (no unscheduled downtime in 6 years from 3 to at one point more than a dozen nodes)
* Excellent hardware - when I've benchmarked real production systems on Linode on a $/perf ratio beats DO hands down
* Excellent support - tickets are generally answered in under 30 minutes and staff are knowledgeable
* It just works(TM)
* Straightforward interface and pricing
* Rock solid network, like bulletproof
* I trust them (after 6 years of the above they have earned it)