is this close enough to what you like to have?

\documentclass{article}
\usepackage[english]{babel}
\usepackage{amsmath}
\usepackage[table]{xcolor}
\usepackage{tabularx, multirow, makecell, rotating} %
\usepackage{enumitem}
\usepackage{etoolbox}
\AtBeginEnvironment{tabular}{%
\setlist[itemize]{nosep,
topsep = 0pt,
partopsep = 0pt,
leftmargin = *,
label = $\bullet$,
before = \vspace{-0.6\baselineskip},
after = \vspace{-\baselineskip}
} }
\makeatletter
\def\@rothead[#1]#2{\thead{\\[-.65\normalbaselineskip] % for centering vertical text
\turn{\cellrotangle}\thead[#1]{#2}\endturn}}
\makeatother
\begin{document}
\begin{center}
\begin{tabular}{ | l | l | p{5cm} |}
\hline
\rowcolor{blue!30}
Cell 1
& Cell 2
& Summary \\ \hline
\multirow{6}{*}{\rothead[c]{very long\\ vertical text}}% text had to be manually
% broken into two lines
& \multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \begin{itemize}
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\end{itemize} \\ \hline
\multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \begin{itemize}
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\end{itemize} \\ \hline
\multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \begin{itemize}
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\end{itemize} \\ \hline
\end{tabular}
\end{center}
\end{document}
addendum (1):
since \rothead
doesn't work well with colortbl
which is called by [table]{xcolor}
for rotating cells Cell 1
and Cell 2
is better to use \rotatebox
from the package graphicx
than \rothead
:
\documentclass{article}
\usepackage[english]{babel}
\usepackage{amsmath}
\usepackage[table]{xcolor}
\usepackage{tabularx, multirow, makecell, rotating} %
\usepackage{graphicx}
\usepackage{enumitem}
\usepackage{etoolbox}
\AtBeginEnvironment{tabular}{%
\setlist[itemize]{nosep,
topsep = 0pt,
partopsep = 0pt,
leftmargin = *,
label = $\bullet$,
before = \vspace{-0.6\baselineskip},
after = \vspace{-\baselineskip}
} }
\makeatletter
\def\@rothead[#1]#2{\thead{\\[-.65\normalbaselineskip]
\turn{\cellrotangle}\thead[#1]{#2}\endturn}}
\makeatother
\begin{document}
\begin{center}
\begin{tabular}{ | l | l | p{5cm} |}
\hline
\rowcolor{blue!30}
\multicolumn{1}{|c|}{\rotatebox[origin=c]{90}{ Cell 1 }}% observe added spaces before and after text in cell
& \multicolumn{1}{c|}{\rotatebox[origin=c]{90}{ Cell 2 }}
& Summary \\ \hline
\multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \begin{itemize}
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\end{itemize} \\ \hline
\multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \begin{itemize}
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\end{itemize} \\ \hline
\multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \multirow{6}{*}{\rothead[c]{very long\\ vertical text}}
& \begin{itemize}
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\end{itemize} \\ \hline
\end{tabular}
\end{center}
\end{document}
which givews

addendum (2):
regarding your additional demand in your comment: to have rotated long text in one column can make trouble to you. it is in multirow
environment, which vertical size is equal to sum of heights of spanned lines. this means, that can happens that you will need to additional (empty) vertical space on the next columns. the result will probably be (very) ugly ...
anyway, the following example has vertical lines in one lines:
\documentclass{article}
\usepackage[english]{babel}
\usepackage{amsmath}
\usepackage[table]{xcolor}
\usepackage{tabularx, multirow, makecell, rotating} %
\usepackage{graphicx}
\usepackage{enumitem}
\usepackage{etoolbox}
\AtBeginEnvironment{tabular}{%
\setlist[itemize]{nosep,
topsep = 0pt,
partopsep = 0pt,
leftmargin = *,
label = $\bullet$,
before = \vspace{-0.6\baselineskip},
after = \vspace{-\baselineskip}
} }
\makeatletter
\def\@rothead[#1]#2{\thead{\\[-.65\normalbaselineskip]
\turn{\cellrotangle}\thead[#1]{#2}\endturn}}
\makeatother
\begin{document}
\begin{center}
\begin{tabular}{ | l | l | p{5cm} |}
\hline
\rowcolor{blue!30}
\multicolumn{1}{|c|}{\rotatebox[origin=c]{90}{ Cell 1 }}% observe added spaces before and after text in cell
& \multicolumn{1}{c|}{\rotatebox[origin=c]{90}{ Cell 2 }}
& Summary \\ \hline
\multirow{10}{*}{\rothead[c]{very long vertical text}}
& \multirow{10}{*}{\rothead[c]{very long vertical text}}
& \begin{itemize}
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\end{itemize} \\ \hline
\multirow{10}{*}{\rothead[c]{very long vertical text}}
& \multirow{10}{*}{\rothead[c]{very long vertical text}}
& \begin{itemize}
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\end{itemize} \\ \hline
\multirow{10}{*}{\rothead[c]{very long vertical text}}
& \multirow{10}{*}{\rothead[c]{very long vertical text}}
& \begin{itemize}
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\item very long text up here right here
\end{itemize} \\ \hline
\end{tabular}
\end{center}
\end{document}
