The Collaborative International Dictionary of English v.0.48:

Spotty \Spot"ty\ (sp[o^]t"t[y^]), a.
   Full of spots; marked with spots.
   [1913 Webster]

WordNet (r) 3.0 (2006):

spotty
    adj 1: having spots or patches (small areas of contrasting color
           or texture); "a field patched with ice and snow"; "the
           wall had a spotty speckled effect"; "a black-and-white
           spotted cow" [syn: patched, spotty, spotted]
    2: lacking consistency; "the golfer hit the ball well but his
       putting was spotty" [syn: spotty, uneven, scratchy]

Moby Thesaurus II by Grady Ward, 1.0:

152 Moby Thesaurus words for "spotty":
   bad, bespangled, bespeckled, blotched, blotchy, brindled, broken,
   broken off, capricious, careening, catchy, cheeseparing, chinchy,
   chintzy, chopped-off, choppy, dappled, decousu, desultory,
   deviative, dirty, disconnected, discontinued, discontinuous,
   discrete, disjunctive, dotted, dotty, eccentric, episodic, erratic,
   exiguous, fitful, flea-bitten, flecked, fleckered, flickering,
   fluctuating, foxed, frecked, freckle-faced, freckled, freckly,
   guttering, halting, herky-jerky, heteroclite, immethodical,
   incoherent, inconstant, infrequent, intermittent, intermitting,
   interrupted, irregular, jagged, jerky, lurching, macular, maculate,
   maculated, marked, meager, miserly, motley, mottled, niggardly,
   noncontinuous, nonlinear, nonsequential, nonserial, nonuniform,
   on-again-off-again, parenthetic, patchy, peppered, piddling,
   piebald, pied, pimpled, pimply, pocked, pockmarked, pocky,
   pointille, pointillistic, polka-dot, poor, punctated, rambling,
   rare, rough, scant, scanty, scarce, scattered, scrappy, scrimping,
   scrimpy, seldom met with, seldom seen, skewbald, skimping, skimpy,
   slim, snatchy, soiled, spangled, sparse, spasmatic, spasmic,
   spasmodic, spastic, spattered, specked, speckled, speckledy,
   speckly, splashed, splattered, splotched, splotchy, sporadic,
   spotted, sprinkled, staggering, stained, stingy, stippled, studded,
   suspended, thin, tight, uncertain, unconnected, unequal, uneven,
   unjoined, unmethodical, unmetrical, unregular, unrhythmical,
   unsettled, unsteady, unsuccessive, unsystematic, variable, veering,
   wandering, wavering, wobbling, wobbly