Removing the offside rule would just kill the mid-field part of the game with soccer. All you would ever have is long balls into each others goal-area, maybe a player or two left in midfield to scramble for loose balls to smack straight back into their opponents areas. There would, potentially, be more goals but this simple rule change would make for an even more boring version of the game I think.

For me Football (soccer) isn't just about goals, but the skill of all of the players on the field. Football can already be tedious when goalkeepers and players play a longball game that inevitably turns into a game of just long kicks either into touch or just up and down the field. Boring. This would simply be so much worse if you removed the offside rule. While the rule can be frustrating, it allows both teams to play more intelligently and tactically.