General synonyms:
* Deplorably
* Miserably
* Gloomily
* Despondently
* Sadly
* Sorrowfully
* Bleakly
* Woefully
* Regrettably
* Regretfully
More specific synonyms:
* For describing a situation:
* Grimly
* Hopelessly
* Desperately
* Poorly
* For describing a performance:
* Abysmally
* Terribly
* Appallingly
* Dreadfully
* For describing a mood:
* Dejectedly
* Dispiritedly
* Despairingly
* Melancholy
The best synonym for "dismally" depends on the specific context of the sentence.