Per baseball prospectus glossary:

 

WARP-1

Wins Above Replacement Player, level 1. The number of wins this player contributed, above what a replacement level hitter, fielder, and pitcher would have done, with adjustments only for within the season. It should be noted that a team which is at replacement level in all three of batting, pitching, and fielding will be an extraordinarily bad team, on the order of 20-25 wins in a 162-game season.

WARP is also listed on a player's PECOTA card. 

 

Basically WARP takes  pitching, hitting, defense and baserunning into account. The "Wins above replacement" are a counting stat, not a rate state, so of course playing time matters.  BUT...if you get a lot of playing time and you suck too much, it's obviously going to work against you.

If I were to rank who I thought have been the most valuable players on this team year to date, without looking up WARP, I really think I would have come up with the same exact order of the top 5.

Webb 4.4

Hudson 3.1

Haren 2.8

Snyder 2.5

Jackson 2.2

Owings 2.0

Young 1.9

Johnson 1.3

Drew 1.2

Reynolds 1.2

Ojeda 1.0

Upton 1.0

Scherzer 0.7

Burke 0.5

Davis 0.4

Byrnes 0.3

Salazar 0.2

Montero 0.1

Gonzalez 0.1

Tracy 0.1

Hammock -0.1

Romero -0.2