The Arrival assignment is a two-parter, and you'll be alone as Shepard for both parts. In the first part you'll be breaking into a Batarian prison to rescue a human captive. The Enemies here are fairly weak, probably due to Shepard being alone. There are a few well-hidden upgrades to find, so keep your eyes peeled.
The second part of the assignment involves an escape from a base. Once again you'll be alone, but the Enemies here are tougher than in part one. The pyros can be especially dangerous, so don't let them get close.