To the newcomer, first-time visitor, and even those who stay longer, there are a few aspects that are quite attractive:
Smiles: Thai people are culturally conditioned to smile (even if they don't want to). When someone smiles at you, you feel welcome.
Very little traffic horn honking: This is really nice, where it seems people don't get angry in traffic. I was at a very busy intersection, dozens of vehicles in all four directions. One bozo tried to turn but got his car jammed in. It took about two minutes of reversing and forwarding to make the turn, and this is right when the light went red for him and green for the other directions. He was literally blocking the intersection for dozens of cars and motorbikes. No one honked at all, everyone just patiently waited. Those kinds of events make you feel like you are "not in a normal country".
"Flexibility" regarding traffic rules: Thai people like to drive they way they want to drive. While that does lead to the second highest mortality rate of accidents, it also provides a certain fluidity regarding driving.
Not noisy (except when drunk/partying): Thai people are not loud, like some other cultures, and shouting across the street is not common. Also, being loud (angry), and throwing things is considered a loss of face so is only done when they have already lost control over their emotions.
Wai (bowing): Thai people wai each other and visitors regularly, which is a pressing of palms together with fingers pointed up, and slight or moderate bowing of the head. This is done with strangers and also younger to older people. Children wai adults and everyone wais older people. Every morning when I go for my run at the local track, there are people there running and walking and we generally wai each other and say hello (sa wa dee krap/ka).
Attractive people: Thai people are quite attractive, and generally dress politely (only in certain tourist ghettos do they dress in a trashy way).
Mai Bpen Rai: Don't worry about it. If someone has a problem or does something then they apologize, it is a common cultural practice to say "don't worry about it" and to smile. This ease of forgiveness (even if someone doesn't feel it, this is the common response), is quite hospitable. I didn't have money to pay for a guesthouse for a day because of some problem with the bank. The guesthouse owner quickly said "mai bpen rai" and I could pay when I got the money.
Kreng Jai: Showing consideration for another. This usually means not disturbing someone (even if they are not behaving correctly). For example, maybe someone is smoking somewhere they shouldn't, even if it bothers people they won't say anything (unless they are told to enforce the rule by an employer). In a negative sense it can get in the way of getting things done and communicating. My old landlady would do this sometimes, even as it is her house she would not want to disturb me to get something fixed inside (and would wait days or weeks before she saw me in passing). You have to tell people "don't kreng jai me" in order so that they communicate more directly or ask you about something that may impose upon you. Also they are likely to not share their direct feelings about something if those feelings are negative. They try and always have a smile (unless there is a serious problem).
Sanuk: Fun-loving. Thai people are very fun-loving. This can be negative in that they don't like to do things that aren't fun, though some are hard-working. By fun-loving they like to get together, eat together, gossip (of course), drink and party, and do fun things. Taking part in Thai festivals (Songkran, Loy Krathong) really highlights the fun-loving aspect.
Safety: Personal safety is generally quite good. There are some places (full-moon parties, anywhere around a lot of alcohol, and single females in some neighborhoods) that are unsafe. When I visited Thailand for the first time in 2004, I was staying in Bangkok and a long-time expat told me he felt more safe walking around Bangkok at midnight than he did walking around in the day in his hometown in America. While there are places in Bangkok to avoid, the likelihood of violent crime is much lower. There is less of a sense of menace. Again, avoid drunk Thai people, or trying to challenge Thais in the event of traffic because road rage in the event where there is a real confrontation can escalate quickly. This may seem like a contradiction with the no-honking but this is a complex culture. Everyone wants to maintain face and peace, but when there seems to be no way to do that, things can get out of hand.
Affordability: Things cost less (in general, though electronics and imported goods can cost more). Food, transportation, housing, Internet access all are less expensive. This is quite hospitable.
Thai food: This can take a bit of getting used to (especially the spiciness), but Thailand has one of the great national cuisines. There are regional specialties and also country-wide goodies. Locally grown and prepared foods are the best. Also, most ingredients are inexpensive and found at all morning markets. Nothing like getting fresh produce, rice soup, and sticks of grilled pork for breakfast at the morning market. Many fresh fruits are cheap and tasty, and inexpensive fresh fruit shakes and smoothies are found everywhere. Coffee is grown in Northern Thailand. And an amazing variety of different kind of prepared dishes, meats, vegetables, fresh fish and seafood, etc., etc.
Warm climate: For those coming from a cold climate, especially in the winter months, there is nothing more hospitable than Thai weather. However it can be damned hot March-May and quite warm (though with refreshing rain showers) from June-mid-Oct.
Thai massage: Inexpensive and extremely relaxing. Also everywhere in Thailand.
There are also annoying/inhospitable aspects of Thai culture, but these elements shine through and charm a lot of visitors, who then return.