Add potatoes and kielbasa and return to a boil. Cover the pot, reduce heat, and let simmer until potatoes are just tender, about 20 minutes.
Add 1 1/2 quarts of water plus onion, garlic, seafood seasoning, salt to taste, and halved lemon (squeeze its juice into the water before tossing in the juiced rinds) to a large roasting pan. Bring mixture to a boil.
Add corn, increase heat to medium-high, and cook, covered, until ears are golden and tender, about 5 minutes longer.
Top stew with shrimp; cover and steam for 3 more minutes.
Turn off heat; gently stir shrimp into hot broth, and let stand, covered, until they are just cooked, about 2 minutes longer.
Serve individual portions with lemon wedges and a bit of melted butter for dipping (if calories aren't a concern). [We halved the recipe here; double or triple amounts to feed a larger group.]