I'm taking a short-cut and am just talking about myself here, so obviously not related to children or teenagers, and many adult learners will have different preferences too.  Anyway, here goes:

I don't particularly like 'lively' classrooms (as a learner, that is). 

I am motivated by pair-work and talking in small groups while sitting in a circle.  I am also motivated by reading and listening tasks, problem solving, and role-plays.  I also often need a bit of time to plan and/or gather my thoughts before doing role-plays, pair-work etc.

I'm demotivated by talking in front of the whole class, standing up and walking or running around, shouting or speaking loudly, playing games, and solo-competition activities (group vs group competition is fun in small doses, though).  With these types of learning I feel awkward or uncomfortable and don't participate attentively or enthusiastically.

The occasional 'lively' activity is okay, but learners like me won't get much out of the learning process if the 'class is lively at all times'. 

The most vital point you need to understand is the thought process of the students. The moment you talk about the English Language, there is a general feeling of frustration and resentment. This basically comes from their interaction with peers or friends, who have never found the English Language Class, motivating and challenging.

Your objective should be to make each session interesting and lively. You need to strike a proper balance between your inputs and your activities. The bottomline is the students should learn the English Language in an interesting and enjoyable way.

It goes without saying, that you ensure, the whole class is treated as one unit and all weak or average students get lot of opportunities and encouragement at your end. The culture that you set for the class as a whole, is very critical for your success. All smarties should be put in their place and you should aim at raising the level of average students, which will give them lot of confidence and self belief.

Lastly, when they start their career, it is ultimately their command over all aspects of the English Language, which will make or break them.

Firstly, I have to point out that I'm not exactly sure what rolandgill's post has to do with the question asked... it seems to me a bit like a definition ... but anyway ...

I think that whether a classroom should include more "lively" activities or more tasks where students can reflect on their learning and the specific focus of the class ultimately depends on the learners. I don't think that getting learners to be "lively" ALL the time is the best way for them to progress in their learning though. It's quite unlikely that every single student will participate fully in such activities, there will be some who are shy and others who would prefer to work things out for themselves or just share their ideas and difficulties with a partner or small group. I think that if reflection is supposed to take place at home, it could lead to loss of some of the input. I mean, if a learner looks over their notes or sits down to do their homework, and then reflects on what they learned in the lesson and suddenly realises there's something they didn't really understand enough to be able to use themselves, then they can't ask the teacher or classmates - and they'll probably forget or not bother if the next lesson has moved on to another topic. Only having lively practice activities may cause learners to focus on the goal of that task, and let accuracy slip a bit in priority - which is obviously fine and can be liberating and motivating, but I'm not convinced that this is really the best strategy to use every lesson.

Of course, I'm interpreting "lively" to mean things like moving around the classroom, competitions, perhaps calling out, using video or audio, and things where learners generally get a bit excited and the struct rules of the classroom are somewhat relaxed.

I suppose that if you mean something else, then my opinion is not entirely relevant. In place of "Liveliness" (in my interpretation of the word), perhaps it's best to provide variation. Students of course should be engaged in the lesson, and the activities should interest them and give them a context in whcih they want to practice so that they are motivated to do so. And using a more "Lively" type activity will always be something some of them look forward to and can be used in a mix with other activities. This way, you cater for more learning styles and promote the retention of new language.

CMF

Besherry: 

But, related to my previous comments, I personally wouldn't look forward to or be deeply interested in a 'lively' class.  It would either make me feel anxious/uncomfortable (I don't want to be in front of the class or mingling) and/or exhausted (especially after a long day at work). If it was always like that, I'd quickly start skipping lessons.

I would look forward to a 'calm-let's-chat-like-we're-sitting-in-a-cafe' style lesson with interesting puzzles and discussion topics.  Interesting doesn't equal lively.  Interesting is so much more; and most importantly, it means different things to different people.

So I'd say:  Variety is important.  (That way you cater to everyone).