Firstly, I think it needs more hazards and terrain features.
Do the sentry boxes provide cover? If so, what kind of cover?
What sorts of hazards and features can the party employ to their advantage?
What does the party gain from this encounter?
Is there any gold or potions around for them to find? Ritual components?
Any items to be recovered from the bodies or found nearby?
Keys?
Any valuable information scrawled anywhere?