Thanks for all the comments.
In my mind 5-morning-a-week nursery class is not 'too much', as I know children go to the school mainly to play - singing & dancing, climbing up and down the stairs to train gross motor skills, doing artwork to train fine motor skills, storytelling time, snack time, theme group play (e.g. last week they played 'fire squad'). 3 hours is easily passed and I think it is certainly GOOD for my kid. The bonus point is that he, so far, LOVES going to school. Every day I ask him if he likes his teachers Ms. So-and-So, he nods with a small smile which makes me feel that the teachers there are pretty good. I believe kids are very sensitive to the difference between those who are loving & caring and those who are harsh & strict. As I work full time, instead of having him stayed at home doing almost nothing than playing with his toys aimlessly or taken down to the park to play with other kids for an hour, enrolling him to a nursery class is good for him. But, only for half day, I wouldn't enrol to a full-day course when he is only as young as 2! (This is another issue I can share later).
The dilemma I am facing is: whether I should get him into other classes at the weekend, say, a toddler football class, a music/dancing class, a Sunday school, swimming class, etc. or simply let him enjoy being at home with his mummy & daddy. As you will see, my intention for enrolling him to these classes is again to let him "play". I have no intention yet to subject him to any pressure to perform this and that well. I may though when he reaches his primary school age. Then on the other hand, I am thinking, am I 'obsessive/pathetic' to always thinking about getting my just 2-year-old to all sorts of extra-activities? Let's not talk about the costs (the costs of all those activities are not cheap, as you all must know), he doesn't have much time left at home and play quietly by himself. But now, after talking to some of you here, I will drop the idea of enrolling him to all sort of activities at the weekend, though I will bring him to a 1.5 hours Sunday school which is just right downstairs of my building.
I think I got a direction now: he is only 2, I may engage him into more activities after he starts his kindergarten say, at least 3~4, but not now when he is only 2.
On another subject, I received a call from a friend who has put her 2-year-old daughter into a full nursery (Mon ~ Frid, from 8:30 ~ 4:30pm). School has started nearly 3 weeks now but his daughter, since then, woke up crying many times a night, screaming, whenever my friend mentioned the word "school", her daughter repeated "no no no - no school, no school..." She is, in my eye, obviously terrified of the thought of going to school. Some kids have stronger adaptability but some have weaker. I am not 100% sure what is the real reason behind her daughter's night waking, screaming, crying behaviour, however, at the back of my mind, I certainly doubt it is because of the sudden change of environment - schooling. To me, sending a 2-year-old kid to a full day school is FAR TOO MUCH - she is suddenly away from her most familiar environment (home) for 8 hours a day! Teachers might not be as caring and loving as a 2-year-old kid expected... I don't think a kid as young as that should face all these new changes to such an extent. What makes thing even worse is that some techers don't treat 2-year-olds as 2-year-olds, they expect them to be very well-behaved or else they shout at them with very harsh tone. This is another reasons I guess, why my friend's daughter refuses to go to school. 2 years old should be treated as 2 years old... they are still BABIES, only a bigger size!