Ja teraz z perspektywy czasu to dziwię się że 20 letni gość w ogóle miał jakieś relacje z 14 letnią (co by nie mówić) dziewczynką ;]

Na ślubach japońskich państwo młodzi się parę przebierają, więc może mieć dwa ;)
Za Mamorka albo Usagi- albo obydwoje?
Mamoru nie był oschły, tylko introwertykiem z rezerwą... Tak naprawdę to szaleje za Usagi...

Mamoru isn’t as cool, sweet, charming and handsome as Seiya Kou, who is the ideal of male despite being really a female and is the one who should be with Usagi;

The Usagi/Seiya pairing was never an option in the series - it was clear for the whole time, who will be the final match for Usagi ("miracle romance" was pretty solid foreshadowing). We actually even got to see their future in R season.

As for who of presented candidates would be better - despite Seiya's (in)famous line "Am I not good enogh?" it was never a competition with Usagi as a prize for the one, who was proved to be better. It was about Usagi's choice and her feelings, which wholly belonged to Mamoru and only to Mamoru. When he is absent in Stars and does not communicate with her, Usagi still believes in their love, writes to him often about everything and even destroys school property by drawing them together.

after two first seasons Mamoru-Usagi relations became boring;
Not so much boring, but stable and solid. They were in courtship stage in first season, later they lost each other, then Mamoru forgot everything - and when they finally got together, these morbid visions appeared and break-up ensued.
In third season they are finally together, in very long-term relationship and, except of Usagi's occasional fits of jealousy, they have no problems.
This may seem boring for some viewers, but I am personally glad they were able to catch a break after all these trials and simply be allowed to be happily together. They support each other and can share everything, as Mamoru says to Chibiusa.
It's true that their initial banter was cute and their emotions during break-up intense. It was, however, great to see more of their ordinary, everyday interactions. It was quite innovative take for a Prince and Princess story, which is normally ended with them getting together and that's end, happily ever after. Usagi declaring that Mamoru is her Prince after he offers her a ride when she's after he offers her a ride when she's carrying shopping bags is the cutest.

this relationship gave birth to Chibiusa, who is an annoying character.
Well, Chibiusa can be annoying, but she has some nice moments and she develops as a person.
Besides, thanks to her they really become great parents.
Other arguments against this pairing, which you can meet:

They are together just because of destiny
It's baffling how people imagine it working - is destiny a cruel matchmaker, putting reluctant people together despite their inclinations?

It is often said that they loathed each other for the whole time, without know knowing about their past. Actually. there is clear attraction between Usagi and Mamoru for some time, before the revelation. They get jealous about each other, find each other attractive and care about each other's opinion. They also start actively seeking each other's company. Mamoru shares with her his past and risks his life to save her. The fact that it took them a little time to fall in love also indicates that not only fate brought them together.
.
And also at the beginning of the R season Mamoru doesn't rememeber anything, but he still still is drawn to her.

The break-up storyline also shows, how much they both want to be together, even when they believe they are not supposed to be together. Futhermore, it proves that destiny wouldn't be able to force them together against their will, as they are broken up for some time..

The ultimate proof of their not being tied by fate is the moment in Stars when Usagi recognises Mamoru's star seed, among millions of other star seeds.

They are completely incompatible
Who should decide whether two people are compatible or not, when they are obviously very happy together, as they declared many times?

Usagi and Mamoru share ideals, values and principles, which is the most important point of compatibility. They may have different tempers, but I'd argue that it is what attracts them to each other and creates sparks in their relations. It also helps them both grow as persons, as Mamoru becomes more open and kind and Usagi matures.

The age gap between them is too big
It's not so big as it is usually claimed - Mamoru at the beginning may be 17-19 - no more than 18 if R movie is to be taken under consideration. So about four years difference isn't really so problematic or unusual.

And age of consent in Japan is 13, so it's completely legal.

Mamoru does not deserve Usagi

Mamoru loves Usagi despite everything, despite all her flaws. He never gets angry at her, when she spilled cookies in his apartament, when she got drunk at the party or when she slapped him in public. In fact, after that he talks with his ex about what he did wrong and runs to her with gift. He also eats what she cooks, including burnt cookies and peppers he dislikes and spends all his money to buy her a designer dress.
How all this should make him unworthy?
Or is it just because he lacks her magical powers? But this should not be the measure of person's worthiness.

A tak co do tego, komu z nich zależy - pamiętajmy, jak Usagi rzuciła Mamoru, by tańczyć z Haruką na balu. Pokazała mu, że jest dla niej drugim gatunkiem....

Rzuciła? O.o Drugim gatunkiem? O.o Ale O Co chodzi???;p ;>
Usagi po prostu była zazdrosna o Mamoru i nie chciała żeby tańczył z Michiru czy z innymi dziewczynami... A jak to zwykle bywa z ludźmi zazdrosnymi, tak i w tym przypadku również --> sama nie widziała nic złego w tańczeniu z Haruką czy innymi facetami;p ;)
O Mamoru Usagi zapomniała tylko na chwilkę, kiedy razem z Minako poznały Harukę, wzięły ją za faceta i obie były "nim" zafascynowane ;) Ale tutaj też nie użyłabym słowa "rzuciła" ;)
A poza tym epizodem to Usagi nie widziała ani Seijuuro, ani Dimonda, ani Seiya, ani innych przystojniaków, którymi były zauroczone pozostałe dziewczyny, dla niej istniał tylko Mamoru Chiba ;)

A tak zasadniczo to się zgadzam, agrest001 - tylko że z reguły demonizuje się Mamoru, a Usagi wybiela - tymczasem ona czasem też miała coś za uszami. Albo jak go walnęła za niewiedzę o jej urodzinach. Ale oczywiście tak naprawdę istnieli tylko dla siebie - jak poznała Harukę, to nawet myśląc, ze to facet, mówiła, że Mamoru jest lepszy :)

a wrzucając list dla Mamoru do skrzynki pocztowej pomyślała o Seyia;)