The original series gets
worse, as everyone who isn't named "William", "Zachary", or "Robot" becomes more or less generic stick figures and the tropes get way too repetitive way too quicky. Season 2 stinks. Season 3 clearly tries a course correction but glaring plot holes and a return to lazy writing after a few episodes (on top of the already lazy plot holes) ruin a lot of it.
That said, if you're of the right mood and/or age, it DOES have a weird camp value, and some cast commentaries on the blu-ray give those episodes a new lease on life, but the show's premise is largely "meh". I like the reboots better* for the fixes put in, but I still don't go out of my way for them either.
I would probably recommend "The Anti-Matter Man", "Visit to a Hostile Planet", and "Time Merchant" as they are highly regarded, even for a kid show that's a bit lower on the bar than other kid shows that treat kids in the audiences a tad better, but before I digress: "Condemned of Space", despite its faults, is a fairly decent escapade and a surprisingly solid season opener that mops the floor with the bulk of season 2's drek - one whose plot has arguably influenced sci-fi since as it is a fairly original idea, even if imperfectly utilized... so plug your proverbial nose and dive into season three, of "Lost in Space".
* shhh, don't tell anyone that