I'm continuing the topic of games here as it is a vast subject. In fact, whole books have been written on this topic.
You asked about using games for explaining grammar. I don't think they're very useful for explaining; my opinion is that they are more useful for practising and reviewing language. I would say the exception to this is when students deduce the rules from sentences (you can see an example of this in the Anti-Grammar Grammar Book).
When using games, your instructions need to be clear and precise. Otherwise students spend time doing the wrong thing. As with all instructions, you need to do a comprehension check. For example, after explaining what to do you can ask the students to explain the game back to you. Another option is to give a demonstration of the game by playing it yourself with a few of the students while the others watch.
You need to choose the games carefully, giving consideration to the age and level of the students. You've asked about I-spy; I think this can be used up to the age of 13. However, I don't think there's a lot of language practice involved in this game. Vocabulary and the alphabet are the main components. Vocabulary is mostly limited to what students can see in the classroom (unless you use pictures) and if students get competitive, they can get involved in obscure language.
Simon Says is good to use with primary age children for revising instructions and parts of the body. You can involve the students more by asking individuals to give instructions that the rest of the class follow.
Hangman can be used at any level and with any age group. It is good for reviewing the alphabet and for activating vocabulary. However, not a lot of language is used and the game can take a long time to complete.
Noughts and crosses can easily be adapted to use with any level or any age group. It can be used to practise pronunciation, spelling, a grammar point, vocabulary. Basically, it's up to the teacher to prepare questions - two or three for each box - on any topic (s)he wishes to review. With children, pictures of individual items can also be used; the children then name the items they see.
If you have any further questions about games, please get in touch again. As I've already said, it's a vast topic and it's difficult to cover all aspects in a small space.