5e version of Combat Reflexes- Too Weak? Too Good?

[the Jester]

Someone pointed out in another thread that Sentinel doesn't emulate the stickiness of a 4e fighter very well because you only get one reaction, so I thought I'd fiddle around with a fix. I don't have the PH yet, so I'm relying on what I've seen online to estimate balance, so I'd appreciate feedback- is this balanced? Too good? Too weak? Does it need an "add 1 to Str or Dex" clause to beef it up?


Combat Reflexes
You are skilled at taking advantage of the openings of your enemies. You gain the following benefits.

• Once per round, you can make an opportunity attack without using your reaction.
• You gain advantage on opportunity attacks.