Not at all / not much
The negative-degree scale: each sets how strong a 'no' is before a negative verb or adjective, from zenzen 'not at all' to sonna ni 'not that much'. nakanaka adds 'just won't', for things that are slow or hard to make happen.
zenzen
(not) at all
全然 ぜんぜん
Means 'not at all' before a negative verb or adjective. With a few words like daijoubu, ii, heiki and chigau it means 'totally' (zenzen daijoubu, zenzen chigau).
imi zenzen wakannai
I don't get it at all.
意味全然わかんない
imi ga zenzen wakarimasen
I have no idea what it means.
意味が全然わかりません
'Zenzen ii' or 'zenzen daijoubu (desu)' means 'totally fine' and is the stock reply to an apology ('no worries at all'). It's heard all the time, in desu/masu speech too, though sticklers object. zenzen + other positive adjectives (zenzen oishii) is slangy, so don't produce it. imi wakannai on its own is also a casual 'that makes no sense'.
anmari
polite amari(not) very; (not) much
あんまり あまり
Means 'not very / not much' before a negative. It is the soft, hedged no, gentler than zenzen.
imi anmari wakannai
I don't really get it.
意味あんまりわかんない
imi ga amari wakarimasen
I don't really get what it means.
意味があまりわかりません
'Anmari…' said alone, trailing off, is a polite 'not really'. Without a negative it means 'too much': anmari da yo! = that's going too far; amari ni takakute kaenakatta = it was so expensive I couldn't buy it. For 'not that …' (sonna ni warukunai), see sonna ni.
hotondo
hardly; almost all
ほとんど
Before a negative it means 'hardly / barely' (hotondo nai). With a positive it means 'almost all' (hotondo owatta).
imi hotondo wakannai
I barely understand it.
意味ほとんどわかんない
imi ga hotondo wakarimasen
I barely understand what it means.
意味がほとんどわかりません
Its meaning flips with the verb: hotondo shitteru = know almost all, hotondo shiranai = know hardly any. As a noun: hotondo no hito = most people; hotondo ga = most of them.
sonna ni
(not) that much; so much
そんなに
Goes before a negative to say 'not as much as you'd think' (sonna ni warukunai = not that bad). Without a negative it means 'so much' (sonna ni tabeta no? = you ate that much?). Said alone, 'e, sonna ni?' reacts to an amount: 'what, that much?', usually surprise, sometimes doubt.
sonna ni warukunai yo
It's not that bad.
そんなに悪くないよ
sonna ni warukunai desu yo
It's not that bad.
そんなに悪くないですよ
konna ni ('this much', about what's here) and anna ni ('that much', about something you both remember) work the same way: konna ni takusan iranai = I don't need this many; anna ni ganbatta noni = after all that effort. anmari can't do the 'not as much as you imply' job.
Learn first: anmari, sonna, -kunai / -ja nai
nakanaka
(not) easily; just won't; quite
なかなか
With a negative it means something just won't happen despite trying or waiting, or is taking ages (nakanaka konai, nakanaka oboerarenai, nakanaka umaku ikanai). Before an adjective it means 'pretty, more than expected' (nakanaka ii, nakanaka muzukashii).
basu, nakanaka konai ne
The bus is taking forever, huh.
バス、なかなか来ないね
basu, nakanaka kimasen ne
The bus is taking a while, isn't it.
バス、なかなか来ませんね
Used as praise, it sounds like you're grading the thing. To a boss, or to the person who cooked, say hontou ni or sugoku instead.