Ah, the sentry: the gift that keeps on giving. In the hands of a good engineer, this little number is a mechanized fountainhead of suppressing fire and mayhem. Managed by an incompetent, it’s a just a big paperweight.
Like so many things in the game, its usefulness comes down to how well it’s actually implemented. Every class has its strong and weak points, and knowing what they are (and how they complement the other classes) is the key to winning. Here are a few observations.
First, the Engineer. He looks a bit like the construction guy from the Village People, and he’s essential to defense. The key word is “defense” here. There are no real “lone wolf” classes in TF2, and though he has a shotgun, the Engineer is woefully undergunned in person-to-person combat.
His job is to set up sentries at chokepoints and let them do the work. Once he’s set up, his only job should be repairing the sentries once enemies figure out where they are and start lobbing rockets and grenades at them. Think Builder Bob, not Rambo.
To that end, put the sentries where a) they won’t be immediately apparent, and b) where they have an effective area of fire. Stick one in the open, and while it’ll do some good, it’s an easy target. Remember, these things take valuable time to build and upgrade. You won’t have that when a Demoman starts carpetbombing the area with grenades. Make them hard for the enemy to reach with explosives. Good spots are in corners at control points and in narrow passages.
Who’s the Engineer’s real nemesis? The Spy. When they’re in disguise, the sentries won’t register them as enemies, and the sappers they lay will destroy any unattended equipment in seconds. Remember, your spot is next to your ordnance, not running around the enemy’s base. Should you be away and a sapper is laid, bear in mind that you can detonate it by pulling up the “build” screen and hitting the left trigger. If the jerk’s close enough, the explosion will kill him, and man, that’s gratifying.