1. Not stimulating
   - unstimulating 
2. Not exciting
   "an unexciting novel"; "lived an unexciting life"

See also: bland, commonplace, dry, excitation, excitement, fervor [US], fervour [Brit, Cdn], flat, humdrum, inflammation, juiceless, prosaic, tame, unexcitingly, unglamorous, unglamourous, uninspired, uninteresting, unmoving, unprovocative, unprovoking, vapid

Antonym: exciting

• unmerited
• unmeritorious
• unmet
• unmethodical
• unmilitary
• unmindful
• unmindfully
• unmindfulness
• unmined
• unmingled
• unmissable
• unmistakable
• unmistakably
• unmistakeable
• unmitigable
• unmitigated
• unmixable
• unmixed
• unmoderated
• unmodernised
• unmodernized
• unmodifiable
• unmodified
• unmodulated
• unmolested