Deadpool... I know many don't like him but I do.  It's just that he doesn't really fit well on this team.  So far I had maybe two laughs from him.  Eveybody on this team seems to be taking everything seriously and I just don't buy into his motivation for being on the team.  Also, it seems that nobody even likes him on the team including the one in charge.  Did they just add him to the team for the sake of it?  I don't even like Archangel but even he has done more to make me like him in this series.

I'm a big Deadpool guy, so I am going to admit my bias upfront, but I think Deadpool fits in well with the team.  His comic relief in this book is stifled in the best way possible, he's not telling the story.  Because the story focuses on the team as a whole, you don't have Deadpool's inner voices clouding the reader with comedy, allowing all characters (including Deadpool) to be taken more seriously.  With his "can do/will do anything for money" attitude, he fits in perfectly with the dirty work expected of the team.  Yeah, when first announced, he didn't seem to fit, but he meshed well in the first story, and maybe they'll elaborate more on why they chose the team in later issues (because frankly, the same question, without the mention of comedy, could be asked about Fantomex).  I think his enhanced healing factor and virtual immortality is his big draw.  They can send him in, guns blazing (the way he likes it) without fear of a casualty. 
 
Spoiler involving around the way issue #4 ended below.
 

CyrixSG, concerning your spoiler, I completely agree with you and had that been the case then I would have said PERFECT... and I probably would have made this topic about Fantomex instead.  It totally would have made more sense and had been funny had Deadpool been the one.
 
I guess I could still make that argument... w/o Fantomex there, it would have freed up room to make all of the rest of the characters cooler.  A lot of the mind tricks that Fantomex was responsible for could have been left for Psylocke... Wolverine could have been the no nonsense go in without caution guy... Archangel (at least for this story) was perfect... and if Deadpool had been the one with the smoking gun then it all would have been tied up perfectly. 
 
Having said all of that, I still enjoy the series and it has only been one story so I guess I'll just sit tight and see where they go with it.

Just got my hands on #4, I honestly thought it was gonna be DP who was gonna make the killshot there, because the last few panels he was doing nothing.

Bet you Fantomex misdirected everyone and let the child Apocalypse live. I don't think Fantomex is that cold-hearted. Psylocke's reaction (or lack thereof) also makes me believe this.

I loved at the end of issue 4 and all the characters were showing remorse and deadpool was just there scratching his head. Great.

Spoilers for Issue 7 follow...
It looks like @Iron_Lag is absolutely right.  Good call as I never saw this coming.  Only thing is I wish I hadn't read this theory before it actually happened because it sort of took the impact away.

Deadpool has been the best he's been in years on this team, Sure he hasn't done a whole lot yet....but this is a team book. I'm sure we'll get a Deadpool heavy story ark at some point.