Ambush Feats (and ratings)
Blue= excellent
Black= average/situational, but excellent
Red= bad
Arterial Strike (CW): This one is varied. The amount of damage each round is minimal, making this feat much more effective when you have a long running battle or need to leave the fight early. The excellent part is that multiple hits stack, so it's not uncommon to have someone losing several hp a round and the price is minimal at only 1d6 damage. The bad part is that it's rather easy to remove, as even a Cure Minor Wounds will do it. Still, most foes in the MM don't have magical healing available to them normally (Fast Healing and Regeneration don't stop it) and even fewer have ranks in Heal.
Concussion attack (CS): I'm not sure how often a -2 penalty on Int and Wis checks/skill checks will help you out. Maybe if you're trying to sneak around the battlefield? Oh wait, you just took a -20 penalty on your hide check by attacking. Yeah, I'd rather have the 2d6 damage and feat slot.
Deafening Strike (CS): 3d6 damage may seem rough, but Deafening is an awesome condition.
Deafened
A deafened character cannot hear. She takes a -4 penalty on initiative checks, automatically fails Listen checks, and has a 20% chance of spell failure when casting spells with verbal components. Characters who remain deafened for a long time grow accustomed to these drawbacks and can overcome some of them.
Yeah, getting the drop on a foe to nail them with that is awesome. Even if you can't get on them before initiative is rolled, it's still nasty to spellcasters. Look at how many spells require verbal components. Oh, and a number of creatures with Blindsense/sight rely on hearing. Deafen them, and they're basically useless. I'd say this is worth the cost.
Disembowling Strike CS):Gloom Strike (DotU):Hamstring (CW): 2d6 damage is the price you pay, but cutting your foes speed in half can make it more difficult for them to do things (like walk out of a Cloudkill). Unfortunately, it loses its appeal at higher levels when more and more enemies have Fly speeds. Situationally a lifesaver, but not necessarily worth having in a feat slot.
Headshot (CS):save? Screw that. This is probably the worst ambush feat printed.
Impeding Attack (CS): 3d6 damage for a -2 penalty on Str and Dex ability and skill checks for a minute. Not bad. Not the most useful, but depending on the build, it can be extremely handy. Your party members may be able to make better use of it than you can.
Maiming Strike (EoE):Merciful Strike (CS):Persistant Attacker (CS): 4d6 damage is a lot to trade, but guaranteeing your first attack next round to be a sneak attack may just be worth it. Of course, one focused on sneak attack should probably have plenty of methods to ensure sneak attacks anyway, so this probably loses out to better options.
Sickening Strike (DotU)Terrifying Strike (DotU):Venemous Strike (DotU):