If your long or descriptive sentences are anything like Stevenson’s, I’ll gladly read every last word of ’em!
SQUIRE TRELAWNEY, Dr. Livesey, and the rest of these gentlemen having asked me to write down the whole particulars about Treasure Island, from the beginning to the end, keeping nothing back but the bearings of the island, and that only because there is still treasure not yet lifted, I take up my pen in the year of grace 17__ and go back to the time when my father kept the Admiral Benbow inn and the brown old seaman with the sabre cut first took up his lodging under our roof.
I remember him as if it were yesterday, as he came plodding to the inn door, his sea-chest following behind him in a hand-barrow–a tall, strong, heavy, nut-brown man, his tarry pigtail falling over the shoulder of his soiled blue coat, his hands ragged and scarred, with black, broken nails, and the sabre cut across one cheek, a dirty, livid white.
~ Robert Louis Stevenson, Treasure Island, Chapter I (at Project Gutenberg)
The first sentence of the story has 90 words, and the second one, a description, has 62. They are both perfectly readable.
Don’t worry about how long or descriptive your sentences are, just as long as the grammar is good and every word counts!