。
Weekdays seem to be relatively uncrowded.
Literal
Weekdays [topic-は] relatively crowded-not appears.
比較的 means 'relatively/comparatively.' 混んでいない is 'not crowded.' ようです at the end is evidential: 'it appears/seems that' — the speaker is making an observation, perhaps from secondhand information or visual evidence. A useful travel-planning sentence.