Kids' emotional growth isn't as steady as the their physical growth. (And even that can come in spurts). One day they'll blow you away with something they say or do, and then they'll seem to take a few steps back.
I tend to take my cues from the kid - if he's telling you he needs a little extra love and affection, pour it on. Smother him with hugs and kisses at the dropoff, and he WILL get bored. I went through a stage where I would spend some extra time with him at the drop off, and I started to say things like "I wish *I* could (fingerpaint or sing songs or whatever it was they were about to do). My work isn't NEARLY as much fun as the stuff YOU get to do. But that's what it's like for grown-ups. <sigh>"
We got into a routine where he would snuggle for a few minutes and then say "Mommy! Go to work!" At first I had to hold him for as long as 5-10 minutes, but eventually, he saw the kids doing something that he wanted to get involved in and he'd squirm down and gleefully say "MOM! Go to work!" and he would run off, happy to be a kid and not a grown up. (Make sure to trudge off, looking a little sad, but don't look TOO miserable or he'll *rescue* you.) Yes, it was a game for him, to be able to say "Mom, go to work!" and run off and do fun stuff. But, even though it was a game, I think it gave him a feeling of having just a little control of his life. (He didn't gt to choose to stay home, he didn't get to choose WHERE he went, or what the activities were that day or WHEN he got to do them. He didn't even choose what he got to eat or whether he needed to nap. But he DID get to say how long he needed mom there. And that really made him happy.)
And you may have people who say "they are fine two minutes after you leave." Well, sometimes they are, and sometimes they are not. SEVERAL times, I went to the front desk of the daycare and watch the monitor for the room. I saw my kid crumpled on the floor where I left him. I waited anxiously, but no one came to comfort him. More than once, I went back to my kid, and usually had a sharp word for the teacher. (It was an expensive daycare, they had NO excuse.)
Yes, and some folks will say "Always be consistent. Always say the same thing when you drop him off, no matter if he's in a good mood or if he's crying." Well, the kid isn't always consistent now, is he? Some days he's fine with me leaving, some days he's not. I was *consistently* there when he told me he needed me.
When in doubt, pour on the love. Smother with hugs, and you will never go wrong, and you'll never regret it.