Do I have to adapt my reviews according to the quality of a journal?
When an article is technically wrong, describes things that have been done dozens of times elsewhere or is just awfully written, then I recommend rejection, no matter the journal. After that, journal guidelines (not the perceived or actual journal "quality") come into play:


Match with the journal's scope
Journal requirements on novelty of ideas (several journals are ok with articles that fill some gap in an otherwise well-understood field, but some very high-profile journals would like to see papers with significant novelty)
Methodological requirements (e.g. some journals require that simulation results are validated against analytic results or measurement results)


So, there is some baseline, but afterwards it depends on the journal scope.