I don't like the way the Summary buffer looks, how to tweak it?
You've got to play around with the variable gnus-summary-line-format. Its value is a string of symbols which stand for things like author, date, subject etc. A list of the available specifiers can be found in the manual node "Summary Buffer Lines" and the often forgotten node "Formatting Variables" and its sub-nodes. There you'll find useful things like positioning the cursor and tabulators which allow you a summary in table form, but sadly hard tabulators are broken in 5.8.8.
Since 5.10, Gnus offers you some very nice new specifiers, e.g., %B which draws a thread-tree and %&user-date which gives you a date where the details are dependent of the articles age. Here's an example which uses both:
(setq gnus-summary-line-format ":%U%R %B %s %-60=|%4L |%-20,20f |%&user-date; \n")
:O Re: [Richard Stallman] rfc2047.el | 13 |Lars Magne Ingebrigt |Sat 23:06 :O Re: Revival of the ding-patches list | 13 |Lars Magne Ingebrigt |Sat 23:12 :R > Re: Find correct list of articles for a gro| 25 |Lars Magne Ingebrigt |Sat 23:16 :O \-> ... | 21 |Kai Grossjohann | 0:01 :R > Re: Cry for help: deuglify.el - moving stuf| 28 |Lars Magne Ingebrigt |Sat 23:34 :O \-> ... | 115 |Raymond Scholz | 1:24 :O \-> ... | 19 |Lars Magne Ingebrigt |15:33 :O Slow mailing list | 13 |Lars Magne Ingebrigt |Sat 23:49 :O Re: `@' mark not documented | 13 |Lars Magne Ingebrigt |Sat 23:50 :R > Re: Gnus still doesn't count messages prope| 23 |Lars Magne Ingebrigt |Sat 23:57 :O \-> ... | 18 |Kai Grossjohann | 0:35 :O \-> ... | 13 |Lars Magne Ingebrigt | 0:56