I'm looking for a new game to play with my wife and some friends, here are the stats:

Number of Players: 4
Weight: Medium (Monopoly being low, Pandemic being Medium and MoM 2nd being heavy)
Time: 1 hour games would be great, 2 hours tops, but enticing replayability
Price: Any
Co-Op preferred
Theme: Murder mystery, not sure how in love they would be with the HP Lovecraft.. but if it's a mystery theme that would go over well.

Is this the type of game that would fit that description?

Yes. The game shines with 4 investigators. It lasts from 30' to 60' according to the expansions you're using. Core set is rather on the light side of the scale; considering for your group MoM 2nd is heavy, then possibly a couple of the ES expansions would be heavy as well (especially Gates of Arkham), but if you go core set, or core set + first expansion (Unseen Forces) you will have quite a few evenings of sheer fun

I'm not sure if this is quite a match for you, @FrogTrigger . It depends on how important the mystery theme is. There isn't really a mystery to be solved, per se, and there is no hidden information to discover. That being said, the characters you play as are considered investigators because they're trying to explore this haunted museum, gathering clue [tokens] and discovering Elder Signs.

Elder Sign does seem to meet the rest of your requirements

• Plays 1-8 (8 can have some downtime, but can still be fun -- and crazy, with the right group of people).
• Weight: Medium
• Time: 1-2 hours
• Price: $35.95
• Cooperative

My wife isn't a fan of the theme so much, but she does enjoy the game. We have some friends that are into euro games and this game is about the lowest end of the spectrum of thematic games that we feel those players can handle. But everyone we've played it with has found it enjoyable, even when we all get devoured.

I think Mansion of Madness would be better for you and your group. While you take on a investigator persona (in Elder Sign) , your objective is to collect the required number of Elder Signs before the Doom counter fills up. To collect these Elder Signs, you have to go to locations that have them and match the symbols on the cards with the symbols on the dice you rolled.