In phone standards the EVO is MUCH bigger than the iPhone. Any person who has not had the opportunity to see the Evo in person and is coming from a Pre or a Blackberry will definitely be shocked (for lack of a better word) by the size.
That said, it is a solid phone and has to be the best built phone that I have seen. The size may take some getting used to, but it is definitely NOT a deal breaker...you have been conditioned to buy/use small phones for the past 10 + years....now carriers are going to start making bigger phones. People want nice, big, bright screens, so they can play their games and surf the net.